CP CU1 Reference Manual COUPLING UNIT FOR LINE IMPEDANCE AND K FACTOR MEASUREMENTS, COUPLING MEASUREMENTS ON POWER LINES AND SIGNAL CABLES AND GROUND IMPEDANCE MEASUREMENTS OF LARGE SUBSTATIONS V1.4
CP CU1 Reference Manual V 1.4 Article Number VESD0671 - Manual Version: CPCU1.AE.4 OMICRON electronics 2005. All rights reserved. This Reference Manual is a publication of OMICRON electronics GmbH. All rights including translation reserved. Reproduction of any kind, e.g., photocopying, microfilming or storage in electronic data processing systems, requires the explicit consent of OMICRON electronics. Reprinting, wholly or in part, is not permitted. This Reference Manual represents the technical status at the time of printing. The product information, specifications, and all technical data contained within this Reference Manual are not contractually binding. OMICRON electronics reserves the right to make changes at any time to the technology and/or configuration without announcement. OMICRON electronics is not to be held liable for statements and declarations given in this Reference Manual. The user is responsible for every application described in this Reference Manual and its results. OMICRON electronics explicitly exonerates itself from all liability for mistakes in this manual. 2
Contents Contents Using This Manual..............................................5 Operator Qualifications and Safety Standards........................... 5 Conventions and Symbols Used..................................... 6 Related Documents............................................... 6 Safety Rules...................................................7 General........................................................ 7 Operating the Measurement Setup................................... 8 Orderly Measures................................................ 9 Disclaimer...................................................... 9 1 Hardware Information..........................................11 1.1 Overview...................................................... 11 1.2 Circuit Diagram of CP CU1........................................ 11 1.3 Operating Controls of CP CU1...................................... 12 1.4 CP CU1 Accessories............................................. 13 1.5 CP GB1 Grounding Box........................................... 14 1.5.1 Description................................................... 14 1.5.2 Shorting the Phases............................................ 17 1.5.3 Changing the Surge Arrestors.................................... 18 1.6 Clamp-on Ammeter.............................................. 20 2 Operation....................................................21 2.1 Measurement Setup............................................. 21 2.2 Operating Principle.............................................. 21 2.3 Configuring CPC 100............................................. 22 2.4 Setting CP CU1................................................. 23 3 Applications..................................................25 3.1 Template Usage................................................ 25 3.2 Safety Instructions for Connecting CP CU1 to Power Lines............... 26 3.2.1 Before Starting................................................ 26 3.2.2 Recommended Current Range Settings............................ 26 3.2.3 Estimating the Open-Line Voltage................................. 27 3.2.4 Connecting the Measurement Setup to Power Lines................... 28 3.3 k Factor Measurement............................................ 30 3.3.1 Why k Factor Measurement?..................................... 30 3
CP CU1 Reference Manual V 1.4 3.3.2 Performing Measurements....................................... 31 3.3.3 Interpretation of Measurement Results............................. 36 3.4 Ground Impedance and Step Voltage Measurement..................... 39 3.4.1 Introduction.................................................. 39 3.4.2 Performing Measurements....................................... 40 3.4.3 Interpretation of Measurement Results............................. 43 3.5 Measurement of Coupling into Signal Cables.......................... 45 3.5.1 Introduction.................................................. 45 3.5.2 Performing Measurements....................................... 45 4 Technical Data................................................51 4.1 CP CU1 Output Ranges.......................................... 51 4.2 CP CU1 Measuring Transformers................................... 51 4.3 CP CU1 Inputs.................................................. 51 4.4 CP GB1 Specifications........................................... 52 4.5 Output Power................................................... 52 4.6 Accuracy...................................................... 53 4.7 Environmental Conditions......................................... 53 4.8 Mechanical Data................................................ 54 4.9 Clamp-on Ammeter (Accessory) Specifications......................... 54 Contact Information / Technical Support..........................55 Index........................................................57 4
Using This Manual Using This Manual This Reference Manual provides detailed information on how to use the CP CU1 coupling unit safely, properly and efficiently. The CP CU1 Reference Manual contains important safety instructions for working with CP CU1, gets you familiar with operating CP CU1, and provides typical application examples. Following the instructions in this Reference Manual will help you to prevent danger, repair costs and possible down time due to incorrect operation. The CP CU1 Reference Manual always has to be available at the site where CP CU1 is used. It must be read and observed by all users of CP CU1. Reading the CP CU1 Reference Manual alone does not release you from the duty of complying with all national and international safety regulations relevant to working with CPC 100 and CP CU1. The regulation EN 50191 "The Erection and Operation of Electrical Test Equipment" as well as all the applicable regulations for accident prevention in the country and at the site of operation has to be fulfilled. Operator Qualifications and Safety Standards Working on overhead lines is extremely dangerous. Testing with CP CU1 must be carried out only by qualified, skilled and authorized personnel. Before starting to work, clearly establish the responsibilities. Personnel receiving training, instructions, directions, or education on CP CU1 must be under constant supervision of an experienced operator while working with the equipment. Testing with CP CU1 must comply with the relevant national and international safety standards listed below: EN 50191 (VDE 0104) "Erection and Operation of Electrical Equipment" EN 50110-1 (VDE 0105 Part 100) "Operation of Electrical Installations" IEEE 510 "IEEE Recommended Practices for Safety in High-Voltage and High-Power Testing" LAPG 1710.6 NASA "Electrical Safety" Moreover, additional relevant laws and internal safety standards have to be followed. 5
CP CU1 Reference Manual V 1.4 Conventions and Symbols Used In this manual, the following symbols indicate paragraphs with special safety relevant meaning: Symbol Description Equipment damage or loss of data possible. Personal injury or severe damage to objects possible. Related Documents The following documents complete the information covered in the CP CU1 Reference Manual: Title CPC 100 User Manual CPC 100 Reference Manual Description Contains information on how to use the CPC 100 test system and relevant safety instructions. Contains detailed hardware and software information on CPC 100 including relevant safety instructions. 6
Safety Rules Safety Rules Before operating the CP CU1 coupling unit, read the following safety rules carefully. If you do not understand some safety rules, contact OMICRON electronics before proceeding. CP CU1 is designated for use with the CPC 100 test system. Therefore observe the safety rules both in this Reference Manual and in the CPC 100 User/Reference Manual when working with CP CU1. Depending on the application and the device under test, specific safety instructions must be observed. Very often the danger coming from the device under test is even higher that the danger from CP CU1 itself. For application specific safety instructions, see 3.2 "Safety Instructions for Connecting CP CU1 to Power Lines" on page 26. General Always observe the five safety rules: Disconnect completely Secure against re-connection Verify that the installation is dead Carry out grounding and short-circuiting Provide protection against adjacent live parts Do not touch any terminals without a visible connection to ground. Before handling CP CU1 or CPC 100 in any way, connect them with a solid connection of at least 6 mm 2 cross-section to ground. Ground CP CU1 as close as possible to CPC 100. Use the CP GB1 grounding box to connect CP CU1 to overhead lines and power cables. For detailed information, see the application specific 3.2 "Safety Instructions for Connecting CP CU1 to Power Lines" on page 26. When using CP GB1, ground it near the place where the connection to the test object is made. Make sure that the grounding stud is in good condition, clean and free of oxidation. Make sure that all studs and cables of CP GB1 are screwed tight. Make sure that the test object s terminals to be connected to CP CU1 do not carry any voltage potential. During a test, the only power source for a test object may be CP CU1 (powered by CPC 100). The only exception are measurements on overhead lines as described in 3 "Applications" on page 25. Do not open the CP CU1 s or CP GB1 s housing. 7
CP CU1 Reference Manual V 1.4 Do not repair, modify, extend, or adapt CP CU1, CP GB1 or any accessories. Use only original accessories available from OMICRON electronics. Use CP CU1, CP GB1 and their accessories only in a technically sound condition and when its use is in accordance with the regulations. In particular, avoid disruptions that could in turn affect safety. Do not use CP CU1 if you have a cardiac pacemaker. Before operating CP CU1 make sure that there is no person with a cardiac pacemaker in the immediate vicinity of the measurement setup. Operating the Measurement Setup Before operating CP CU1, CPC 100 and, when used, CP GB1, ground them as described in "General" on page 7. When using CP GB1, ground it near the place where the connection to the test object is made. Make sure that the grounding stud is in good condition, clean and free of oxidation. Life threatening voltages up to 600 V can appear on all CP GB1 s contacts and on all clamps and cables connected to CP CU1 during the test. Keep safe distance from them. Before handling CP CU1 or CP GB1 in any way (even before setting the current range switch), make sure that the device under test (e.g. overhead lines or power cables) are well grounded (e.g. by closing the grounding switch) near the measurement setup. Power CP CU1 only from the CPC 100 s EXT. BOOSTER output. Use only booster cables supplied by OMICRON electronics. Ensure that the short-circuit bar is always plugged in the CP CU1 s I AC output whenever the output is not connected to the I AC input of CPC 100. Connect the CP CU1 s I AC output exclusively to the I AC input of CPC 100. Before connecting CP CU1 with CPC 100, turn off CPC 100 either by the POWER ON/OFF switch or the Emergency Stop button. Set the current range switch on the CP CU1 s front panel only when CPC 100 is turned off and the test object is grounded. In addition to the above safety rules follow the application specific 3.2 "Safety Instructions for Connecting CP CU1 to Power Lines" on page 26. 8
Safety Rules Orderly Measures The CP CU1 Reference Manual or alternatively the e-book in PDF format has always to be available on the site where CP CU1 is being used. It must be read and observed by all users of CP CU1. CP CU1 may be used only as described in 3 "Applications" on page 25. Any other use is not in accordance with the regulations. The manufacturer and/or distributor is not liable for damage resulting from improper usage. The user alone assumes all responsibility and risk. Following the instructions provided in this Reference Manual is also considered part of being in accordance with the regulations. Disclaimer If the equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be impaired. 9
10 CP CU1 Reference Manual V 1.4
Hardware Information 1 Hardware Information 1.1 Overview CP CU1 is a coupling unit designated for measurements with the CPC 100 test system mainly on overhead lines and power cables. Typical applications include line and cable impedance measurements, measurements of k factors, mutual coupling of power lines, measurements of coupling between power lines and signal cables, and ground impedance measurements. The CP GB1 grounding box (see 1.5 "CP GB1 Grounding Box" on page 14) available as an accessory from OMICRON electronics is a surge arrestor unit protecting the operating staff and equipment from high-voltage hazards during measurements on overhead lines and power cables in case of unexpected events on the power line. 1.2 Circuit Diagram of CP CU1 Figure 1-1: "Circuit Diagram of CP CU1" below shows the principal circuit diagram of the coupling unit. Figure 1-1: Circuit Diagram of CP CU1 Fuse 30 A Power transformer Current range switch IAC (0 2.5A) Surge arrestor BOOSTER CT I OUT (0 100 A) Voltmeter V1 AC (0 30 V) V SENSE (0 600 V) Surge arrestor VT 11
CP CU1 Reference Manual V 1.4 1.3 Operating Controls of CP CU1 The front panel of CP CU1 provides the following functional elements: BOOSTER input for connecting with the CPC 100 s EXT. BOOSTER output Current range switch for setting the current range of CP CU1 Voltmeter for measuring the voltage at the test object s terminals I OUT current output I AC output for measuring the output current using a CT (current transformer) with the 100 A : 2.5 A transformation ratio The output is to be connected with the I AC input of CPC 100. V SENSE input for measuring the voltage at the test object s terminals V1 AC output for measuring the voltage at the test object s terminals using a VT (voltage transformer) with the 600 V : 30 V transformation ratio The output is to be connected with the V1 AC input of CPC 100. Short-circuit bar for shorting the I AC output whenever the output is not connected to the I AC input of CPC 100 Equipotential ground terminal for grounding CP CU1 close to the position of the operating staff Figure 1-2: "Front Panel" below shows the CP CU1 s functional elements. Figure 1-2: Front Panel Equipotential ground terminal Location to I AC output V1 AC output V SENSE input store the shortcircuit bar Fuse 30 A BOOSTER input Current range switch Voltmeter I OUT output 12
Hardware Information 1.4 CP CU1 Accessories The following accessories are delivered with the CP CU1 coupling unit: Table 1-1: CP CU1 Accessories Accessories Booster cable Description Power connection from the CPC 100 s EXT. BOOSTER output to the CP CU1 s BOOSTER input V1 AC coax. cable Connection from the CPC 100 s V1 AC input to the CP CU1 s V1 AC output 4 Banana cable Connection from the CPC 100 s I AC input to the CP CU1 s I AC output and connection from the CP CU1 s V SENSE input to the Kelvin clamps voltage sense outputs 2 Kelvin cable Connection from the CP CU1 s I OUT output to the current feed-in point (usually at CP GB1) Grounding cable Connection from the CP CU1 s equipotential ground terminal to the substation ground Short-circuit bar A bar for shorting the CP CU1 s I AC output when the output is not connected to the I AC input of CPC 100 13
CP CU1 Reference Manual V 1.4 1.5 CP GB1 Grounding Box 1.5.1 Description The CP GB1 grounding box (see Figure 1-3: "CP GB1 Grounding Box" below) is a surge arrestor unit for connecting CP CU1 to the test object. If high voltage appears for a short time on the test object s terminals, an arc discharges the voltage and distinguishes without destroying the grounding box. If the arc persists for a longer time period, the surge arrestor insulator melts and the terminals are short-circuited to ground, thereby protecting the operating staff, CP CU1 and CPC 100. Figure 1-3: CP GB1 Grounding Box Other stud standards available optionally L1 line stud A/L1/red Equipotential ground stud L2 line stud B/L2/yellow L3 line stud C/L3/blue Caution: The CP GB1 grounding box must be used for measurements on overhead lines or power cables. The CP GB1 grounding box is available for three different ground connection types: cylindrical grounding studs of 16 mm diameter or ball studs of 20 mm and 25 mm (1 inch) diameter. The grounding socket clamp is needed for secure ground connection of CP GB1 to the substation ground. The grounding socket clamps compatible with the grounding studs in the substation are given in Table 14
Hardware Information 1-2: "Grounding Studs and Socket Clamps" below. For ordering information, contact OMICRON electronics sales office. When ordering CP GB1, choose one connection set; additional connection sets are available optionally. Table 1-2: Grounding Studs and Socket Clamps Grounding Stud in the Substation 16 mm cylindrical grounding stud Proper Grounding Socket Clamp 16 20 mm grounding socket clamp (shipped with the 16 mm cylindrical and 20 mm ball CP GB1 s studs) 12 mm 20 mm ball grounding stud 25 mm ball grounding stud 25 mm grounding socket clamp (shipped with the 25 mm CP GB1 s studs) 16 mm 15
CP CU1 Reference Manual V 1.4 Figure 1-4: Screwing the CP GB1 s Studs Caution: Depending on the type of grounding studs in the substation, the appropriate connection set and socket clamp have to be used. Connecting socket clamps of one type to a grounding point of another system is highly dangerous on both the connection of the grounding set to CP GB1 and the connection of CP GB1 to the grounding point in the substation. The 16 to 20 mm socket clamps are designed and tested for fault currents up to 26.5 ka, the 25 mm (1 inch) socket clamp for fault currents up to 30 ka, both for a maximum duration of 100 ms. On locations where higher fault currents are possible, CP CU1 and CP GB1 must not be used. For transportation, the CP GB1 s studs are usually removed. If this is the case, mount them onto CP GB1 using the delivered wrench and screw them tight (see Figure 1-4: "Screwing the CP GB1 s Studs" on page 16). 16
Hardware Information Figure 1-5: Three-Lead Cable 1.5.2 Shorting the Phases A three-lead cable is delivered with CP GB1 for shorting all phases for L1 L2 L3-E measurements (see Figure 3-5: "Zero-Sequence Impedance Measurement" on page 34, Figure 3-8: "Ground Impedance and Step Voltage Measurement" on page 41, Figure 3-13: "Measurement with the Loop Between Parallel Lines and Ground" on page 48 and Figure 3-14: "Calibration with the Loop Between Parallel Lines and Ground" on page 49). Figure 1-6: Shorting the Phases To short the phases, connect the line studs of CP GB1 as shown in Figure 1-6: "Shorting the Phases" below. 17
CP CU1 Reference Manual V 1.4 Figure 1-7: Surge Arrestors 1.5.3 Changing the Surge Arrestors The surge arrestors of CP GB1 can permanently short-circuit the CP GB1 s terminals to ground if overvoltage appears on the terminals. Even short transients can cause a discharge and, if the energy is too high, possibly damage the surge arrestor. Defective surge arrestors can result in erroneous measurement results. If the measurement results obtained using CP GB1 differ considerably from the expected values, check the surge arrestors using CPC 100 as follows. Apply a voltage of 500 V for at least 10 seconds using the VWithstand test card from the resistance test cards. Set a test current of 0.01 A. If the current is exceeded, an error message is displayed. In this case the surge arrestor under test is defective and you have to replace it. If no message is displayed, the surge arrestor is intact. For detailed information on this test, see the CPC 100 Reference Manual. Repeat the test for all three studs A/L1, B/L2 and C/L3. Replace defective surge arrestors only by spare parts from OMICRON electronics (see Figure 1-7: "Surge Arrestors" below). For ordering information, contact OMICRON electronics sales office. Note: Before changing the surge arrestors, check whether there is a fault that caused the problem and remove it. 18
Hardware Information Figure 1-8: Opening the Surge Arrestor Chamber To replace a surge arrestor: 1. Disconnect CP GB1 completely and observe the five safety rules in "Safety Rules" on page 7. 2. Open the surge arrestor chamber using a 22 mm wrench by removing the contact screw (see Figure 1-8: "Opening the Surge Arrestor Chamber" on page 19). Contact screw 3. Turn CP GB1 upright and move the stud over the surge arrestor chamber until the surge arrestor falls out. 4. Replace the defective surge arrestor by the spare one. 5. Screw the contact screw very tight (torsional moment of 15 20 Nm). 19
CP CU1 Reference Manual V 1.4 Figure 1-9: Clamp-on Ammeter 1.6 Clamp-on Ammeter A clamp-on ammeter for AC 50/60 Hz (see Figure 1-9: "Clamp-on Ammeter" below) is available from OMICRON electronics as an accessory. For ordering information, contact OMICRON electronics sales office. The clamp-on ammeter provides the following features: Hold function Battery check Auto power off Bar display Voltmeter Ohmmeter Contact check with beeper 20
Operation 2 Operation 2.1 Measurement Setup The measurement setup consists of the CPC 100 test system, of the CP CU1 coupling unit and, in case of measurements on overhead lines and power cables, of the CP GB1 grounding box. Figure 2-1: "Measurement Setup" below shows the functional block diagram. Caution: CP CU1 must be connected to the test object through the CP GB1 grounding box for measurements on overhead lines or power cables. For these applications, connect the measurement setup by following 3.2 "Safety Instructions for Connecting CP CU1 to Power Lines" on page 26. Figure 2-1: Measurement Setup Dangerous zone V1 AC IAC IAC V1 AC CP GB1 IOUT (optional) CPC 100 CP CU1 Device under test EXT. BOOSTER BOOSTER V SENSE 2.2 Operating Principle CP CU1 is a coupling unit controlled by the CPC 100 test system via the BOOSTER interface. CP CU1 provides programmable current signals at the I OUT output and facilitates measuring of the output current and the voltage at the test object s terminals. The current range of 10 A, 20 A, 50 A or 100 A is set by the CPC 100 software (see 2.3 "Configuring CPC 100" on page 22) and the current range switch on the front panel of CP CU1 is set manually by the user (see 2.4 "Setting CP CU1" on page 23). The output current and the voltage at the test object s terminals connected to the CP CU1 s V SENSE input are processed by the coupling unit for measuring with CPC 100. The output current is transformed by a current transformer with the transmission ratio 100 A : 2.5 A and the secondary transformer winding wired to the I AC output. The transformed current at the I AC output is measured via the 21
CP CU1 Reference Manual V 1.4 I AC input of CPC 100. The test object s voltage is transformed by a voltage transformer with the transmission ratio 600 V : 30 V and the secondary transformer winding wired to the V1 AC output. The transformed voltage at the V1 AC output is measured via the V1 AC input of CPC 100. The measurements are performed frequency selective, i.e. only signal components at the generated frequency different from the mains frequency are analyzed. Due to the high-power disturbances at the mains frequency, the spectral components around the mains frequency and its harmonics are filtered out. For detailed information on the frequency selective measurement, see "Getting Started with Quick: The frequency selective measurement" in the CPC 100 Reference Manual. 2.3 Configuring CPC 100 Figure 2-2: Options Window Note: The minimum CPC 100 software version required is V 1.4. If you have an earlier version installed, upgrade the software from the CD-ROM delivered with your CP CU1. CPC 100 must be configured for CP CU1. To configure CPC 100: 1. Press the Options view selector button. The Options window with the Device Setup tab selected (see Figure 2-2: "Options Window" below) opens. 2. Select CU1 from the External booster combo box. The CT and VT settings are set according to the built-in current and voltage transformers automatically. 3. Press the Test Card View view selector button and insert the Quick (default), Sequencer or Ramping test card. Figure 2-3: "Quick Test Card Window" below shows the setting using the Quick test card as example. 22
Operation Figure 2-3: Quick Test Card Window Output Range combo box Measured Quantities combo box 4. Open the item list from the Output Range combo box. The item list displays the CU1:10A, CU1:20A, CU1:50A and CU1:100A CP CU1 relevant current ranges. 5. Select VT sel and/or CT sel from the Measured Quantities combo boxes when measuring with the CP CU1 s built-in voltage and current transformers to account for their transformation ratio. 6. Select the current range you want to use. 2.4 Setting CP CU1 Set the current range of CP CU1 using the current range switch (see 1.3 "Operating Controls of CP CU1" on page 12) to the value configured by the CPC 100 software. Caution: Set the current range switch on the CP CU1 s front panel only when CPC 100 is turned off and the test object is connected to ground with closed grounding switch near the measurement setup. Note: Current range settings on the test card and on the CP CU1 s front panel must be the same. 23
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Applications 3 Applications 3.1 Template Usage The test procedures running on the measurement setup are controlled by templates available on the CPC Explorer CD-ROM shipped with your CP CU1 or in the customer area of the OMICRON electronics home page http://www.omicron.at. The templates are pairs of XML documents and Microsoft Excel templates designed by OMICRON electronics for designated applications. The XML templates are predefined test procedures, often with comments, that run on CPC 100 and guide the user through the test. Once completed, the XML file is saved, downloaded to the PC using CPC Explorer and then loaded into the corresponding Microsoft Excel template. There the results are post processed and a final test report is generated. The template pairs facilitate and speed testing with CP CU1 and the evaluation of results. Note: Some template pairs allow version control. If an error message appears after loading the XML template, use a template pair of the same version. To run a test procedure according a template: 1. Using CPC Explorer, upload the XML template for the intended application from the PC to CPC 100. 2. Open the template on CPC 100. 3. Run the test procedure according to the template. 4. After completing the test procedure, save the test in a new file. 5. Using CPC Explorer, download the test results from CPC 100 to your preferred working directory on the PC. 6. Open the corresponding Microsoft Excel template by double-clicking the *.xlt file in the folder labeled with the test procedure name. A Microsoft Excel workbook appears. 7. Click the Load XML-File button and open the *.xml file saved in your preferred working directory before to load the test results. 8. After all worksheets are filled with data, the test results are calculated. 25
CP CU1 Reference Manual V 1.4 3.2 Safety Instructions for Connecting CP CU1 to Power Lines 3.2.1 Before Starting Caution: A lightning discharge to the line under test can cause injury or possibly death of the operating staff. Do not connect the measurement setup to overhead lines if there is a possibility of a thunderstorm over any part of the lines to be measured. Caution: Connecting the measurement setup to overhead lines with a life parallel system bring about high-voltage hazards. It is strongly recommended to take all parallel lines out of service before proceeding. Before connecting CP CU1 to overhead lines or power cables (further on referred to as power lines), you must estimate the open-line voltage as follows. Follow the instructions below exactly and sequentially to protect yourself from high-voltage hazards. In addition to the following safety instructions, observe "Safety Rules" on page 7. 3.2.2 Recommended Current Range Settings The highest current range allowed by the open-line voltage (see 3.2.4 "Connecting the Measurement Setup to Power Lines" on page 28) provides the best measurement accuracy. However, depending on the length of the power line under test, this setting may result in CPC 100 overload due to low driving voltage. As a rule of thumb, the current range required for the power line length is given in Table 3-1: "Recommended Current Range Settings" below. Set the current range switch of CP CU1 to the value according to the table. Table 3-1: Recommended Current Range Settings Line Impedance Line Length Current Range Compliance Voltage 0 1.6 Ω 0 2 km/0 1.5 miles 100 A 50 V 0.8 8 Ω 1 10 km/0.5 5 miles 50 A 100 V 4.0 40 Ω 5 50 km/3 30 miles 20 A 250 V > 16 Ω > 20 km/15 miles 10 A 500 V 26
Applications 3.2.3 Estimating the Open-Line Voltage To estimate the open-line voltage: 1. Switch off, short-circuit and ground the power line on both sides using an installed grounding switch or, if no grounding switch is available on site, using grounding cables (further on, the grounding switch or these extra grounding cables are referred to as grounding switch). 2. Make sure that the connection to ground at the far end of the power line is not removed during the complete test procedure. 3. In addition to the grounding switch, ground the line at the near end using a grounding set consisting of three cables rated for the maximum short-circuit current possible on the line. This connection is called working ground further on. 4. Open the grounding switch at the near end of the power line and measure the current through the working ground using a clamp-on ammeter on all three phases. 5. Close the grounding switch. 6. Calculate the estimated open-line voltage after removal of the grounding cables as follows: V est [V] = I meas [A] 0.4 [Ω/km] 2 l line [km] (Eq. 3-1) or V est [V] = I meas [A] 0.64 [Ω/mile] 2 l line [miles] (Eq. 3-2) where V est [V] is the estimated open-loop voltage in volts, I meas is the highest measured current in ampers, 0.4 [Ω/km] = 0.64 [Ω/mile] is the constant of a typical overhead line per wire and l line [km] and l line [miles] is the length of the line in km and miles respectively. Caution: If the estimated open-line voltage is > 500 V, stop. The measurement is not possible due to high-voltage hazard. Try to take parallel lines out of service. 250 500 V, the measurement is possible only in the 10 A range. 100 250 V, the measurement is possible in the 10 A or 20 A range. 50 100 V, the measurement is possible in the 10 A, 20 A or 50 A range. < 50 V, the measurement is possible in all current ranges. 7. If the current range allowed by the estimated open-line-voltage is lower as the current range set according to Table 3-1: "Recommended Current Range Settings" on page 26, set the current range switch of CP CU1 to the value allowed by the open-line voltage. 27
CP CU1 Reference Manual V 1.4 Caution: During the grounding switch at the near end of the power line is open, the area around CP GB1 in the range of 5 m/15 ft and around CP CU1 in the range of 2 m/5 ft is a dangerous zone due to high-voltage and mechanical hazards. Do not enter the dangerous zone. Keep the grounding switch open for a time as short as possible. Caution: If you see or hear anything uncommon in the test equipment, e.g. noise of electrical discharge or lightening of surge arrestors, close the grounding switch before touching the measurement setup. 3.2.4 Connecting the Measurement Setup to Power Lines If the estimated open-line voltage (see 3.2.3 "Estimating the Open-Line Voltage" on page 27) allows measurement in the current range you want to use, connect the measurement setup to the power line as follows: 1. Make sure that the grounding switch is closed. 2. Connect CP GB1 to ground using the delivered cable near the place where the connection to the line is made. Make sure that the grounding stud is in good condition, clean and free of oxidation. Caution: Depending on the type of grounding points in the substation, the appropriate connection set and socket clamp have to be used. Connecting socket clamps of one type to a grounding point of another system is highly dangerous on both the connection of the grounding set to CP GB1 and the connection of CP GB1 to the grounding point in the substation. The 16 to 20 mm socket clamps are designed and tested for fault currents up to 26.5 ka, the 25 mm (1 inch) socket clamp for fault currents up to 30 ka, both for a maximum duration of 100 ms. On locations where higher fault currents are possible, CP CU1 and CP GB1 must not be used. 3. Disconnect the grounding cables from the ground (the grounding switch is closed!) and connect them to the CP GB1 s line studs. 4. Position CP CU1 at a minimum distance of 5 m/15 ft from CP GB1. 5. Position CPC 100 at a minimum distance of 5 m/15 ft from CP CU1 and 10 m/30 ft from CP GB1. 6. Ground CP CU1 using a cable of at least 6 mm 2 cross-section close to CPC 100 and the position of the operator. 7. Connect CP CU1 with CP GB1 as shown in Figure 3-1: "Wiring the Measurement Setup" on page 29. 28
Applications Figure 3-1: Wiring the Measurement Setup Connection using grounding sets on site L3/C L2/B L1/A 8. Ground CPC 100 using a cable of at least 6 mm 2 cross-section close to the position of the operator. 9. Connect CP CU1 with CPC 100 as shown in Figure 3-1: "Wiring the Measurement Setup" above. 10.Mark the area around CP GB1 in the range of at least 5 m/15 ft and around CP CU1 in the range of at least 2 m/5 ft as dangerous zone. 11.Open the grounding switch and read the voltmeter on the CP CU1 s front panel from outside of the dangerous zone. Caution: If the voltmeter s reading is > 500 V, stop. The measurement is not possible due to high-voltage hazard. 250 500 V, the measurement is possible only in the 10 A range. 100 250 V, the measurement is possible in the 10 A or 20 A range. 50 100 V, the measurement is possible in the 10 A, 20 A or 50 A range. < 50 V, the measurement is possible in all current ranges. If the open-line voltage allows measurement, proceed as described in the respective "Performing Measurements" section of the following applications. Caution: Make sure that the grounding switch is always closed when no measurement is performed and especially when the wiring is modified or the current range switch of CP CU1 is set. 29
CP CU1 Reference Manual V 1.4 3.3 k Factor Measurement 3.3.1 Why k Factor Measurement? On most modern secondary distance protection relays, the value of the positivesequence (line) and zero-sequence (line-to-ground) impedance or the ground impedance matching factor (k factor) is required to make the relay settings. The line impedance can be readily calculated but the chosen values for the ground impedance often do not match the actual conditions. The accuracy of these settings is crucial to the operation of the relay because they directly affect the reach of the different protection zones e.g. in case of a line-to-ground fault. Measurements show that in significant number of cases the k factor of the measured lines is set more than 20% from its actual value. This can result in zone under- or overreach and consequently, the selectivity is lost. This situation is particularly relevant to underground power cables. The k factors are line parameters independent of the fault location describing the ratio of the line and ground impedances. The following k factor definitions are commonly used: The complex ratio of the ground impedance Z E and the line impedance Z L k L = Z E /Z L = (Z 0 /Z 1 1)/3, (Eq. 3-3) the complex ratio of the zero-sequence impedance Z 0 and the positivesequence impedance Z 1 (see Figure 3-2: "Zero-Sequence Impedance Definition" below) k 0 = Z 0 /Z 1 (Eq. 3-4) and a couple of real values R E /R L (Eq. 3-5) X E /X L (Eq. 3-6) where R E and X E are the real and imaginary parts respectively of the ground impedance and R L and X L are the real and imaginary parts respectively of the line impedance. 30
Applications Figure 3-2: Zero-Sequence Impedance Definition The k factor is an important setting of distance protection relays. The precision of this setting affects the accuracy of distance protection relays dramatically. The k factor can be calculated, but the calculation results give only a rough estimate of the actual value. As a wrong k factor setting can cause worse power quality, higher risk to lose the system stability and loss of power supply, k factor measurements are essential for fast, selective and reliable distance protection. Because there are usually strong disturbances by other lines in service, measurement at the mains frequency is not feasible. All measurements running according to the templates are done below and above the mains frequency and the results are interpolated. From these results the positive- and zero-sequence impedances as well as the k factor in various formats are calculated. 3.3.2 Performing Measurements Connect the measurement setup to the overhead lines or power cables under test following 3.2 "Safety Instructions for Connecting CP CU1 to Power Lines" on page 26. Note: For line length below 5 km/3 miles it is recommended to connect the V SENSE input of CP CU1 as close as possible to the VT of the line to reduce the additional impedance of the current feed in the path. For longer lines, you can connect the V SENSE input with the Kelvin clamps directly on CP GB1. 31
CP CU1 Reference Manual V 1.4 In the course of the k factor test procedure, the following measurements are performed: Line-to-line impedance measurements: L1-L2, L1-L3, L2-L3 (Figure 3-3: "Line-to-Line Impedance Measurements" below shows the L1-L2 measurement as example.) Figure 3-3: Line-to-Line Impedance Measurements Far end Near end Overhead line V1 AC IAC CPC 100 EXT. BOOSTER IAC V1 AC IOUT CP CU1 BOOSTER V SENSE CP GB1 32
Applications Line-to-ground impedance measurements: L1-E, L2-E, L3-E (Figure 3-4: "Line-to-Ground Impedance Measurements" below shows the L1-E measurement as example.) Figure 3-4: Line-to-Ground Impedance Measurements Far end Near end Overhead line V1 AC IAC CPC 100 EXT. BOOSTER IAC V1 AC IOUT CP CU1 BOOSTER V SENSE CP GB1 33
CP CU1 Reference Manual V 1.4 Zero-sequence impedance measurements: L1 L2 L3-E (see Figure 3-5: "Zero-Sequence Impedance Measurement" below) Short the three phases with the delivered three-lead cable as shown in Figure 1-6: "Shorting the Phases" on page 17. Figure 3-5: Zero-Sequence Impedance Measurement Far end Near end Overhead line V1 AC IAC CPC 100 EXT. BOOSTER IAC V1 AC IOUT CP CU1 BOOSTER V SENSE CP GB1 The test procedure is controlled by templates available on the CPC Explorer CD-ROM shipped with your CP CU1 or in the customer area of the OMICRON electronics home page. For detailed information on the templates and instructions how to use them, see 3.1 "Template Usage" on page 25. It is recommended to use the same test current for all measurements. To find out the highest test current possible, start the test procedure with the measurement featuring the highest impedance, i.e., the L1-L3 measurement on power cables and the L1-E measurement on overhead lines. 34
Applications After wiring the measurement setup to the line under test proceed as follows: 1. Configure CPC 100 as described in 2.3 "Configuring CPC 100" on page 22 for the CP CU1 s current range set by the current range switch. Caution: The configured current range must not exceed the limit by the open-line voltage. 2. Choose the XML template for the mains frequency (e.g. "Line Imp CU1 60Hz.xmt" for the 60 Hz mains frequency) and open the template. Caution: Open the grounding switch at the near end before making the test and keep it open only during the measurement. Close the grounding switch after the test and before reconnecting the measurement setup. 3. Run the test procedure. The following measurements are performed: Line-to-line measurements: L1-L2, L1-L3, L2-L3 For each measurement, connect the I OUT and V SENSE inputs of CP CU1 to the corresponding CP GB1 s line studs. Line-to-ground-measurements: L1-E, L2-E, L3-E For each measurement, connect the I OUT and V SENSE inputs of CP CU1 to the corresponding CP GB1 s line studs. Zero-sequence impedance measurement: L1 L2 L3-E 4. If an overload of CPC 100 occurs, reduce the test current or set a lower current range and run the test procedure once again. Lower test currents at the two highest frequencies are recommended. 5. Save the test procedure as a file on CPC 100. 6. Download the test file from CPC 100 to the PC using CPC Explorer. 7. Load the test file into the Microsoft Excel template. The measurement results are displayed. The measurement of mutual coupling of two power lines is performed in a similar way. All three phases of both systems under test are connected together and grounded at the far end of the line. The current I I is fed into all the phases of the system I and the voltage U II is measured on the near end of the system II which is not grounded here. The mutual coupling factor for the relay II is then given by k M0 = (U II /I I )/Z LII (Eq. 3-7) 35
CP CU1 Reference Manual V 1.4 3.3.3 Interpretation of Measurement Results To interpret the results of line impedance measurements correctly, you have to know details about the overhead line or power cable under test. You will find below some useful notes about how to interpret the measurement results. Usually, the resistive part of the line impedance is relatively constant over the L1-L2, L1-L3 and L2-L3 as well as L1-E, L2-E and L3-E measurements. If the measurement results differ considerably, typically contact problems are the reason. In some cases, the grounding switches at the far end of the line are not as good as necessary for the measurement. Additional grounding cables could help to avoid the contact problems. For the lines under test shorter than 5 km/3 miles, do not connect the V SENSE input of CP CU1 with the Kelvin clamps, but rather use additional clamps directly on the wires of the power line. The inductive part of the line impedance increases with the distance between the lines. This is documented by the measurement results stored in an example file delivered with the line impedance templates (see the marked results in Figure 3-6: "Measurement Results" on page 37). The measured overhead line with the shortest distance between the lines L1 and L3 is shown in Figure 3-7: "Measured Overhead Line" on page 38. Note: For each line of measurement results there is a separate overload indication top right on the CPC 100 s screen (or in the report) explained below. No overload indication means no overload during that step of the measurement sequence. Dotted overload indication means that there was an overload during that step of the measurement sequence but not all the time. Solid overload indication means a permanent overload during that step of the measurement sequence. 36
Applications Figure 3-6: Measurement Results 37
CP CU1 Reference Manual V 1.4 Figure 3-7: Measured Overhead Line L2 L1 L3 The L2-E measurement features the lowest X component because the line is very close to the ground wire. The X component of the L3-E measurement is decreased by a parallel system taking course close to L3 on the other side of the tower. Short-circuiting of the parallel system during the measurement would have increased the effect and would have lead to erroneous results because this is not the normal operating condition. The interpretation of the result of zerosequence impedance measurement is more difficult. Some methods for verifying it are shown below. Several intermediate results are hidden in the Microsoft Excel template due to their minor importance. However, by clicking on the "+" symbol on the left (see the lines 32 and 51 in Figure 3-6: "Measurement Results" on page 37) you can view the individual k factor results for each line. If the individual measurements are very close to each other and close to the overall k factor, the measurement is most likely correct. Broadly spread results with the average value close to the overall k factor value indicate a very asymmetrical line under test but the results are most likely correct. If the individual k factor measurements differ considerably from each other, the relay should be set to a value smaller than the average k factor to avoid zone overreaches. 38
Applications Another interesting effect can be observed when measuring power cables. If the screen or shield is very close to the conductors but the conductors are relatively wide from each other, the inductive part of the line-to-line measurements is higher than the inductive part of the line-to-ground measurements, resulting in a negative X component of the calculated impedance Z E. This seemingly strange result is explained as follows. Recalling (see 3.3.1 "Why k Factor Measurement?" on page 30) that the zero-sequence impedance is given by Z 0 = Z 1 + 3Z E (Eq. 3-8) and hence Z E = (Z 0 Z 1 )/3 (Eq. 3-9) where Z 1 is the positive-sequence impedance and Z E is defined as a difference between the line-to-ground loop measurement and a half of the line-to-line loop measurement, the X component of Z E can become negative. 3.4 Ground Impedance and Step Voltage Measurement 3.4.1 Introduction A good substation grounding system is crucial to prevent people injury and damage of equipment. International standards such as DIN VDE 0101/CENELEC HD637S1, IEEE Std 80-2000 or IEEE Std 81-1983 give guidelines how to measure such impedances. This application describes the measurement of large substations. Smaller grounding systems could be tested without connection to an existing overhead line or power cable and therefore the use of CP CU1 and CP GB1 would not be necessary. However, the procedure is the same when injecting the current into a long wire directly from the 6 A AC output. Anyway, when injecting the current into a test probe, special safety measures are required to avoid hazards when people approach the test probe. The current-voltage method as called in CENELEC HD637S1 or fall of potential method as called in IEEE standards is a good solution to measure the ground impedance of a substation. Before starting the test procedure, take one overhead line or power cable leaving the substation under test out of service and ground it at the far end. Feed a current via this power line into a remote ground. For larger substations, a distance of the remote ground of at least 5 km/3 miles is recommended, the minimum distance is 10 times the size of the grounding system. Then measure the voltages with a test probe at various distances 39
CP CU1 Reference Manual V 1.4 around the substation. If possible, choose the measurement points in a 90º angle (bird s-eye view) relative to the current path. In any case, avoid measuring close (<60º) to the current path. For an accurate estimate of the step voltage, set the measurement points as close as 1 m/3 ft to the substation and to each other. The step voltage is calculated for a certain fault current. Enter the highest possible fault current for the substation under test in the relevant field of the Microsoft Excel template. Measurement data at a large distance (typically three times the length of the substation) from the substation allow the calculation of the overall substation ground impedance Z ground as defined in VDE 0101. 3.4.2 Performing Measurements To measure ground impedance and step voltage: 1. Connect the measurement setup to an overhead line or a power cable leading from the substation under test following 3.2 "Safety Instructions for Connecting CP CU1 to Power Lines" on page 26. 2. Short the three phases with the delivered three-lead cable as shown in Figure 1-6: "Shorting the Phases" on page 17. 3. Connect one pin of the CPC 100 s V1 AC input to the ground substation ground, the other pin to a test probe as shown in Figure 3-8: "Ground Impedance and Step Voltage Measurement" on page 41. The V SENSE input and the V1 AC output of CP CU1 are not used in this application. The voltage is measured directly using the V1 AC input of CPC 100. 40
Applications Figure 3-8: Ground Impedance and Step Voltage Measurement 90º V1 AC IAC CPC 100 EXT. BOOSTER IAC IOUT CP CU1 BOOSTER CP GB1 The test procedure is controlled by templates available on the CPC Explorer CD-ROM shipped with your CP CU1 or in the customer area of the OMICRON electronics home page. For detailed information on the templates and instructions how to use them, see 3.1 "Template Usage" on page 25. Using the CPC 100 s Sequencer test card, the test procedure runs without user interaction, performing the recommended six measurements per test probe position. Caution: Do not touch the test probe without insulating gloves outside of the substation area. In case of a high-current ground fault within the substation during the test, considerably high voltages could arise in any wire connected to the substation and leading away from it. 41
CP CU1 Reference Manual V 1.4 After wiring the measurement setup to the line proceed as follows: 1. Configure CPC 100 as described in 2.3 "Configuring CPC 100" on page 22 for the CP CU1 s current range set by the current range switch. Caution: The configured current range must not exceed the limit by the open-line voltage. 2. Choose the XML template for the mains frequency (e.g. "Ground Imp CU1 60Hz.xmt" for the 60 Hz mains frequency) and open the template. 3. Select the "Enter Distance Here" card from the template. 4. Select "Save as Default" to reuse this card later on. 5. Stick the test probe into the ground at the specified distance from the substation and proceed from short to long distances. Recommended distances for the step voltage measurement are 1 to 15 m in 1 m steps (3 to 45 ft in 3 ft steps) in the first file and 15 to 30 m in 1 m steps (45 to 90 ft) in the second file. For the ground impedance measurement, 1, 2, 5, 10, 20, 50, 100, 150, 200 m and continuing in 100 m steps (5, 10, 20, 50, 100, 200, 500, 750, 1000 ft and continuing in 250 ft steps) seem to be a good choice. You can measure the distance for this application conveniently with a commercial GPS device. Note: Make sure that the measurement points take course in a 90º angle (bird s-eye view) relative to the current path and, if possible, avoid additional overhead lines or power cables as well as current paths. 6. Start the test card for the current test point. 7. Label the test card with the distance in units m or ft without blanks, e.g. "10m" or "30ft". 8. Add one Sequencer test card for every test point you want to measure. 9. Proceed with step 6 as long as you want to measure at another distance. 10.Save the test procedure as a file on CPC 100. Note: It is recommended to save at most 15 test cards in one file, but having more files is possible. 11.Download the test file(s) from CPC 100 to the PC using CPC Explorer. 12.Load the test file(s) into the Microsoft Excel template. The ground impedance and the step voltage are displayed as a function of the distance from the substation. Note: If there are more files, load one after another. 42
Applications 3.4.3 Interpretation of Measurement Results Ground Impedance Measurement Due to the inductance of the feed-in line, a considerable part of the current I out injected into the ground does not flow back through the ground but through the ground wire or the line shield. This current I shield has to be subtracted from I out and, consequently, the ground impedance is given by Z ground = V meas /(I out I shield ) (Eq. 3-10) This effect is compensated by the current reduction factor r as defined in the CENELEC HD637 S :1999. A field in the XML template allows setting the current reduction factor between 0.01 and 1.00 (1.00 means no current compensation). For 110 kv overhead lines, the standard gives typical values of r = 0.98 for steel ground wires and down to 0.60 for steel/aluminum ground wires. For current feeding via power cables, the r factor can be as low as 0.01. The effect of the current I shield can be eliminated by disconnecting the line shield or the ground wire of the feed-in line. If the disconnection is not possible, it is recommended to measure the current I shield with a clamp-on ammeter and to calculate the current reduction factor as r = 1 I shield /I out (Eq. 3-11) The example file delivered with the templates includes measurement results for a terrain approaching the optimum. Figure 3-9: "Ground Impedance vs. Distance for a Terrain Approaching Optimum" on page 44 shows a graph displayed after loading the example file into the Microsoft Excel template. The voltage between the grounding system under test and the test probe (and hence the ground impedance) increases slowly until it reaches an approximately constant value. This limit value corresponds to the ground impedance Z ground, the impedance of the substation against the "rest of the world". In the example considered, Z ground is approximately 60 mω. 43
CP CU1 Reference Manual V 1.4 Figure 3-9: Ground Impedance vs. Distance for a Terrain Approaching Optimum Figure 3-10: Ground Impedance vs. Distance for a Difficult Terrain In some cases, measurement results shows peaks and drops until an area free of buildings and buried conductors or pipes is reached. Until then, erroneous results can be obtained. Figure 3-10: "Ground Impedance vs. Distance for a Difficult Terrain" below shows typical measurement results obtained under such conditions. The graph shows a peak due to a street lamp close to the test probe. The street lamp was connected to a protective ground wire approaching the location of the remote grounding system. Voltage drops can be observed when the measurement points are set close to objects (i.e. towers of power lines leaving the substation under test) connected to the grounding system under test. In a difficult terrain, the measurement results may show no noticeable trend until values converging to a constant are obtained. Consequently, the terrain analysis on site is of highest importance. Setting the measurement points close to the line injecting the current results in erroneously high measured values. An area within the angle of at least 60º relative to the line should be avoided. 44