MRI (Mk3) Digital Overcurrent & Earth Fault Relay

Transcription

1 MRI (Mk3) Digital Overcurrent & Earth Fault Relay Belle Vue Works Boundary Street Manchester M12 5NG Tel: Fax: Internet Address 20/7/99 Page 0 Issue 1

2 Contents 1. INTRODUCTION APPLICATION FEATURES AND CHARACTERISTICS DESIGN CONNECTIONS Analogue input circuits Output relays Remote data communication FRONT PANEL Display LED Indicators Push Buttons CODE JUMPERS Password Programming Reset Function WORKING PRINCIPLES ANALOGUE CIRCUITS DIGITAL CIRCUITS POWER SUPPLY PHASE FAULT DIRECTIONAL FEATURE (OPTIONAL) EARTH FAULT DIRECTIONAL FEATURE (OPTIONAL) Earth fault direction feature for isolated or compensated earthed networks Isolated Systems Compensated System Solidly Earthed System Resistive Earthed System REQUIREMENTS FOR THE MAIN CURRENT TRANSFORMERS BLOCKING INPUT RESET INPUT RESET DELAY & DWELL TIME Reset Delay Dwell Time CIRCUIT BREAKER FAILURE PROTECTION (T CBFP ) DISPLAY OF PICK-UP EVENT DISPLAY OF MEASURING VALUES AS PRIMARY QUANTITIES (I PRIM PHASE) DISPLAY OF EARTH CURRENT AS PRIMARY QUANTITY (I PRIM EARTH) DISPLAY OF RESIDUAL VOLTAGE UE AS PRIMARY QUANTITY (U PRIM /U SEC ) OPERATION AND SETTING LAYOUT OF THE CONTROL ELEMENTS RELAY SETTING PRINCIPLES Password protected parameter adjustment SETTING PROCEDURE Starting current for phase overcurrent relay (I>) Time current Characteristic for phase overcurrent relay (CHAR I>) Tripping time delay or time multiplier for phase overcurrent relay (ti>) Current setting for high set stage of phase overcurrent relay (I>>) Tripping time delay for high set stage of phase overcurrent relay (ti>>) Starting current for earth fault relay (IE>) Time Current characteristic for earth fault relay (CHAR IE) Tripping time delay or time multiplier for earth fault relay (tie>) Current setting for high set stage of earth fault relay (IE>>) Tripping time delay for high set stage of earth fault relay (tie>>) /7/99 Page ii Issue 1

3 Earthing type COS/SIN Measurement SOLI/RES Setting Residual Earth Fault Voltage (VE) Residual Earth Fault Voltage Measurement Method Earth Fault Response Nominal frequency Assignments Of The Blocking Inputs Blocking Of Protection Functions Programming Of Output Relays Parameter Switch Fault Recorder Number of the fault recordings Adjustment of trigger occurrences Pre-trigger time (T pre ) Adjustment of the clock Communication Settings Slave Address Baud Rate Parity Reset Setting (For Inverse Time Overcurrent Function) Reset Setting (For Inverse Time Earth Fault Function) Dwell Time Relay Characteristic Angle (RCA) Pick Up Value For Residual Voltage U E Setting Summary INDICATION OF MEASURED VALUES AND FAULT DATA Indication of measured values Measured Values as a Primary Value Indication of fault data Fault Recording TEST TRIP RESET Hand reset Reset input SETTING VALUE CALCULATION Low set stage High set stage Characteristic curve Low set stage time multiplier/time delay High set stage time delay RELAY CASE INDIVIDUAL CASE RACK MOUNTING TERMINAL CONNECTIONS TEST AND MAINTENANCE POWER ON TESTING THE OUTPUT RELAYS AND LEDS CHECKING THE SET VALUES SECONDARY INJECTION TEST Test Equipment Checking the input circuits and measured values Checking the operating and resetting values of the relay Checking the relay operating time Checking the high set element of the relay Example of a test circuit for MRI relay with directional feature Test circuit earth fault directional feature Checking the external blocking and reset functions Test of the CB failure protection PRIMARY INJECTION TEST MAINTENANCE /7/99 Page iii Issue 1

4 9. TECHNICAL DATA MEASURING INPUT CIRCUITS AUXILIARY POWER SUPPLY COMMON DATA SETTING RANGES AND STEPS Definite time phase overcurrent relay Inverse time phase overcurrent relay Direction unit for phase overcurrent relay Direction unit for earth fault relay INVERSE TIME CHARACTERISTICS Inverse time Equations OUTPUT CONTACT RATINGS TYPE TESTS HOUSING TERMINAL CONNECTION DETAILS ORDER FORM /7/99 Page iv Issue 1

5 1. Introduction. The application of powerful microprocessors opens a new chapter for power system protective relaying. The digital processing of measured values and the ability to perform complex arithmetic and logic operations, give digital protection relays significant performance and flexibility improvements over their traditional analogue counterparts. Additional advantages - very small power consumption, adaptability, self-supervision, fault diagnosis through fault data recording, smaller physical construction and selectable relay characteristics - all combine to allow the implementation of accurate and highly reliable protection schemes at a significantly reduced financial burden. The development of microprocessor based protective relays and their introduction into the market has been stimulated by the recent trend to replace analogue with digital equipment. This modern trend has prompted the development of a new P&B protective relay family - the MR relay series. This comprehensive family of protection relays can satisfy the demands of even the most complex protection schemes: MRI - Overcurrent Relay (Independent time/i.d.m.t + earth + directional facilities) MRI-V - Voltage Dependent Overcurrent Relay MSP - Voltage or Overcurrent (I.D.M.T + earth + directional) Relay MREF - Restricted Earth Fault Relay MRAR - Auto-Reclosing Relay MRMF - Mains Failure Relay MRVT - Voltage Protection MRFT - Frequency Protection MROS - Vector Surge MRNS - Negative Sequence Relay MRRP - Power Relay MRCS - Check Synchronising Relay MRFF - Field Failure Relay MRDG - Differential Relay The superiority of digital protective relaying over traditional analogue devices, as embodied by the MR relay family, is summarised by the following features: Integration of many protective functions in a single compact case High accuracy owing to digital processing Digital relay setting with very wide setting ranges and fine setting steps Comfortable setting procedure through extensive human - relay dialogue Measured values and fault data indication by means of alpha-numeric display Data exchange with DCS/SCADA by means of RS485 Operational reliability through self-supervision The digital overcurrent and earth fault relay MRI, was designed as a universal overcurrent relay for applications in medium voltage networks. A similar, but simplified version, the MIRI, with reduced functions and without display, is also available. Similarly for protection against undervoltage, overvoltage and neutral voltage displacement, a reduced function non-display relay, the MIRV is available. To complement the MR series, a range of Auxiliary, Timing and Tripping devices are also available. The MSP range of relays were added to create a new series of single pole, competitive overcurrent or voltage protection relays. They have the added feature of a large LCD Display, enabling greater display of data. 20/7/99 Page 1 Issue 1

6 2. Application. The MRI is a universal digital multifunctional relay used for overcurrent and/or earth fault protection in medium voltage networks with ring mains, parallel feeders or doubly infed lines. The protective functions of the MRI are summarised as follows: Selectable protective functions between : - Definite time overcurrent relay - Inverse time overcurrent relay Inverse definite minimum time (IDMT) overcurrent relay with the following selectable characteristics in accordance with BS 142 and IEC : - Normal Inverse - Very Inverse - Extremely Inverse - RI-Inverse - Long Time Inverse High set overcurrent unit with instantaneous or definite time function Two stage overcurrent relay both for phase and earth faults Built in direction unit for application to ring main or parallel feeders with adjustable relay characteristic angle (Optional) Built in earth fault direction unit for application to power system networks with solid/resistive neutral earthing or isolated/arc suppressing coil (Peterson Coil) neutral earthing. (Optional) Two stage (Low and High Set) earth fault protection with definite or inverse time characteristics Reset time selectable for inverse time characteristics ("pecking faults") Furthermore, the MRI relay can be employed as back-up protection for distance and differential protective relays. 20/7/99 Page 2 Issue 1

7 3. Features and characteristics. Complete digital processing of the sampled measured values Digital filtering of measured values using discrete fourier analysis to suppress high frequency harmonics and d.c component induced by faults or system operations Extremely wide setting ranges with fine setting steps Two Parameter Sets Unauthorised user access control through password protection User defined password Continuous self-supervision of software and hardware Outstanding design flexibility for easy selection of appropriate operational scheme for numerous applications Numerical display of setting values, actual measured values and their active/reactive components and memorised fault data etc. Display of measuring values as primary quantities Blocking e.g. of high set element (e.g. for selective fault detection through downstream overcurrent protection units after unsuccessful Auto Reclose) Storage of trip values and switching off time (tcbfp) of 5 fault occurrences Recording of up to eight fault occurrences with time stamp Display of Date and Time Serial data communication facilities via RS485 interface with NETWORK GOLD or Modbus RTU (Note For Modbus no fault recording is available) Wide voltage range for DC or AC power supply Withdrawable modules with automatic short circuit of C.T. inputs Circuit Breaker Failure Protection Programmable Output Relays Suppression of indication after an activation 20/7/99 Page 3 Issue 1

8 4. Design Connections. Application Diagram; Overcurrent and Earth Fault Directional L 1 L 2 L 3 S u p p ly 1 2 C A S E E x te r n a l R e s e t B lo c k in g In p u t L N L P 2 S P O W E R S U P P L Y P 1 S I1 I2 I3 IE R E L A Y 1 R E L A Y A lte rn a tiv e E a rth in g I1 I2 I3 N V 1 V 2 V 3 M R I-IE D R E L A Y 3 R E L A Y 4 S E L F S U P E R V IS IO N - R S G n d T y p ic a l E a r th in g S h o w n Application Diagram; Overcurrent and Only Earth Fault Directional L 1 L 2 L 3 S u p p ly 1 2 C A S E External ResetBlocking Input L N L 15 I1 P O W E R V 1 S U P P L Y I2 I3 N V 2 V 3 RELAY P 2 P 1 S 2 S 1 Alte rn a tive E a rth in g I1 I2 I3 RELAY 2 RELAY 3 RELAY 4 SELF SUPERVISIO N C B C T I E M R I-I-E X - R S G n d Typical Earthing Show n /7/99 Page 4 Issue 1

9 Application Diagram; Overcurrent and Earth Fault L 1 L 2 L 3 S u p p ly 1 2 C A S E External ResetBlocking Input L N L P O W E R S U P P L Y P 2 P 1 S 2 S I1 R E L A Y I2 I3 R E L A Y IE M R I-IE R E L A Y 3 R E L A Y 4 S E L F S U P E R V IS IO N - R S G n d T yp ic al E a rth in g S h o w n Application Diagram; Overcurrent and Earth Fault -Special Export Version L 1 L 2 L 3 S u p p ly 1 2 C A S E External ResetBlocking Input L N L P O W E R S U P P L Y P 2 P 1 S 2 S I1 R E L A Y I2 I3 IE M R I-IE K R E L A Y 2 R E L A Y 3 R E L A Y 4 S E L F S U P E R V IS IO N - R S G n d T yp ic a l E a rth in g S h o w n FO R TRIP /ALARM FUNC TIO NS, RE FER TO /7/99 Page 5 Issue 1

10 Application Diagram; Earth Fault Directional L 1 L 2 L 3 S u p p ly 1 2 C A S E External R esetb locking Input L N L P O W E R S U P P L Y 1 5 L L 2 L 3 R E L A Y N A lte rn a tiv e E a r th in g C B C T 2 7 I E T y p ic a l e a rth in g s h o w n 2 8 M R I-E D M R I-E X R E L A Y 4 S E L F S U P E R V IS IO N - R S G n d Application Diagram; Earth Fault L 1 L 2 L 3 S u p p ly 1 2 C A S E External ResetB locking Input L N L P O W E R S U P P L Y R E L A Y C B C T 2 7 I E 2 8 M R I-E R E L A Y 4 S E L F S U P E R V IS IO N - R S G n d T y p ic a l e a rth in g s h o w n /7/99 Page 6 Issue 1

11 Application Diagram; Overcurrent L 1 L2 L3 S upply 1 2 C AS E External ResetBlocking Input L N L PO W E R SU PPL Y 31 P 2 P 1 S 2 S I1 I2 RELAY 1 RELAY I3 RELAY RELAY 4 M R I-I - SELF SUPERVISION R S G nd Typical Earthing Show n FOR TRIP /ALARM FUNC TIONS, REFER TO Application Diagram; Overcurrent Directional L 1 L 2 L 3 S u p p ly 1 2 C A S E E x te rn a l R e s e t B lo c k in g In p u t L N L P 2 S P O W E R S U P P L Y P 1 S I1 I2 I3 R E L A Y 1 R E L A Y I1 I2 V 1 R E L A Y V 2 R E L A Y 4 A lte rn a ti v e E a r th in g I3 N V 3 M R I-ID - S E L F S U P E R V IS IO N R S G n d T y p ic a l E a r th in g S h o w n /7/99 Page 7 Issue 1

12 Application Diagram; Overcurrent Directional Alternative Application Diagram using a 'v' connected voltage transformer 2 phase input. L 1 L 2 L 3 S u p p ly 1 2 C A S E E x te r n a l R e s e t B lo c k in g In p u t L N L P 2 S P O W E R S U P P L Y P 1 S I1 I2 I3 R E L A Y 1 R E L A Y I1 I2 V 1 R E L A Y V 2 R E L A Y 4 N u e tra l N o t C o n n e c t e d I3 N V 3 M R I-ID - S E L F S U P E R V IS IO N R S G n d T y p ic a l E a r th in g S h o w n Analogue input circuits. The constantly monitored measuring values are galvanically decoupled, filtered and finally fed to the analogue/digital converter. The protection unit receives these analogue input signals of the phase currents I1, I2, I3 and residual current IE, and phase voltages V1, V2, V3 with a star point, each via separate input transformers. The residual voltage Ve, required for MRI units with earth fault directional facility, is formed internally in the secondary circuit of the voltage transformers. Where only the earth fault directional facility is required (ie phase fault directional facility unused) the residual voltage from an existing open delta winding may be directly connected across L1 & N Output relays. The MRI has five output relays, with single or dual pole change-over contacts as detailed in the previous diagrams. With the exception of Relay 5, which is used only for self supervision output and which is normally energised, the other Relays (1 to 4) are programmable to the users specification (see Section ). The factory default settings are given in table shown in section In the alarm mode, alarm outputs operate upon energisation. 20/7/99 Page 8 Issue 1

13 Remote data communication. As an option, the MRI may have an RS485 interface for remote data communication with a control centre. The unit provides the following information: Measured phase fault current values Measured earth fault current values Status signals Self supervision alarm signal Actual measured current values Relay settings Phase fault signalling Earth fault signalling There is a choice in the communication protocol of the MRI relay. Both Modbus RTU and NETWORK GOLD is available. Unfortunately fault recording is not available in a relay with Modbus RTU Front Panel. The front panel of the MRI comprises the following operation and indication elements: Display. Alphanumeric display (4 Digits) 5 push buttons for setting and other operations Up to 23 LEDs for measured value indication and setting The measured and set values, and recorded fault data, are shown alphanumerically on the display. The meaning of the displayed values is easily interpreted from the LED indicators on the front panel. See Section 6.4. for more details. 20/7/99 Page 9 Issue 1

14 LED Indicators. The LEDs to the left of the display indicate measuring or tripping values. The purpose of the corresponding LED is identified by the adjacent inscription, (e.g. L2 for current in phase 2). The full list of LEDs are as follows:- LED Indicates L1 Current Phase 1 L2 Current Phase 2 L3 Current Phase 3 E Earth Current Date And Time I P Active Component I Q Reactive Component Relay Characteristic Angle / Direction * RS Serial Address FR Fault Recording P2 Parameter Switch C.B. Circuit Breaker Fail Protection I> Pickup Current For Phase Overcurrent CHAR I> Time Current Characteristics for Phase O/C t I> Tine Delay or Time Multiplier for Phase O/C I>> Current Setting for High Set Element t I>> Time Delay for High Set Element I E > Pickup Current for Earth Fault Element CHAR I E Time Current Characteristics for E/F t IE> Time Delay or Time Multiplier for E/F I E >> Current Setting for High Set Element of E/F t IE>> Trip Delay for High Set Element of E/F U E > Residual Voltage * For forward direction this LED is illuminated GREEN, and For reverse direction this LED is illuminated RED. Up to ten LEDs support the setting menu selection. They are arranged at the characteristic points on the setting curves. Upto five are for phase fault characteristic and upto five are for earth fault characteristic. Each indicate the corresponding menu point selected. 20/7/99 Page 10 Issue 1

15 Push Buttons. The front panel contains five push buttons used for setting, measuring and other user functions. The individual setting and measuring values can be selected in turn by pressing the <SELECT/RESET> push button. This button also resets the relay if pressed for approximately 3 seconds. The <UP> and <DOWN> push buttons are for incrementing and decrementing any selected parameter. Continuous pressing of these push buttons will cause the parameter to change at an increased rate. The <ENTER> push button is used to transfer the indicated value to the internal parameter memory. An unintended or unauthorised change of the selected parameter can be avoided through the password protection facility. The <TRIP> push button is used to test the output relay circuits, both for tripping and signalling. This operation is also password protected Code Jumpers. Behind the front panel of the MRI are two code jumpers used to preset the following functions: Password programming Reset functions Front Board The following figure shows the position and designation of the code jumpers. Note. If you have a Surface Mount Board (with Wide range power supplies) there will be two extra jumpers. These jumpers are used to choose the input voltage for the external reset and the blocking input. The two jumpers should always be the same. Jumper 4 Input voltage upto 240V Jumper 5 Input voltage upto 110V Code Jumper Code Jumper ON Code Jumper OFF J3 J2 J1 Pre Wide Range Power Supply. Post Wide Range Power Supply. 20/7/99 Page 11 Issue 1

16 Password Programming. The MRI relay is normally delivered with the preset password " ", it can be reprogrammed using the removable code jumper J1. After power on and the pressing of any push button, the MRI relay enquires for a new password with the text "PSW?" appearing on the display. A new password is then entered by pressing a combination of <SELECT/RESET>, <UP>, <DOWN> or <ENTER>, as chosen by the user. After the new password has been given, the relay module is extracted from its case and code jumper J1 removed Reset Function. Code jumper J3 - OFF All output relays will be reset automatically after tripping, once the fault has been cleared. Code jumper J3 - ON All output relays remain activated and must be reset manually by pressing the <RESET> push button, after the fault has been cleared. Summarising the coding possibilities Code jumper Function Code jumper Position Operation Mode J1 Password OFF ON Normal position Password programming J3 Reset OFF ON Output relays will be reset automatically. Output relays will be reset manually. 20/7/99 Page 12 Issue 1

17 5. Working Principles Analogue Circuits. The incoming currents from the external current transformers are converted to internal signals in proportion to the currents, via the internal input transducers and shunt resistors. The noise signals caused by inductive and capacitive coupling are suppressed by an analogue RC filter circuit. The analogue signals are fed to the A/D converter of the micro-processor and transformed to digital signals through sample-hold circuits. The analogue signals are sampled with a sampling frequency of 800 Hz, namely a sampling rate of 1.25 ms for every measured quantity. In order to achieve a sensitive earth current measurement, an operational amplifier is connected to the earth current input circuit before the analogue signal enters the A/D converter. The incoming voltages from the external voltage transformers are fed to operational amplifiers through the input transducers and RC filters. The analogue voltage signals are transformed into a logical binary signal, which is used as a reference signal to detect fault direction. The residual voltage needed for earth fault direction is formed internally from the secondary circuits of the input transducers Digital Circuits. The essential component of the MRI relay is a powerful micro-controller. All of the operations, from the analogue digital conversion to the relay trip decision, are carried out by the microcontroller digitally. The relay program, located in EPROM, allows the CPU of the micro-controller to calculate the three phase currents and earth fault current in order to detect a possible fault. For the calculation of the current value, an efficient digital filter, based on the Fourier Analysis (DFFT - Discrete Fast Fourier Transformation), is applied to suppress high frequency harmonics and DC components caused by fault induced transients or other system disturbances. The actual calculated current values are compared with the relay settings. When a current exceeds the starting value the unit starts the corresponding time delay calculation. When the set time delay has elapsed, a trip signal is given. The relay setting values for all parameters are stored in EEPROM, so that the actual relay settings cannot be lost, even in the event of auxiliary supply interruption. The micro-processor is supervised through a built in "Watch-dog" timer. Should a failure occur the watch-dog timer resets the microprocessor and gives an alarm signal via the self supervision output relay Power Supply. A wide range auxiliary power supply is available: Vaux = 16V to 360V DC 16V to 270V AC 20/7/99 Page 13 Issue 1

18 5.4. Phase Fault Directional feature (optional). An integral directional element is available within the MRI-IED, MRI-ED, MRI-I-EX & MRI-ID relays. In order to achieve the reliable detection of fault current flow direction, the relay uses an internal quadrature connection. With this method; the reference voltage for phase current I1 is taken from phase to phase voltage V23, the reference voltage for phase current I2 is taken from phase to phase voltage V31, the reference voltage for phase current I3 is taken from phase to phase voltage V12, This method ensures that whilst the voltage may decrease on the faulted phase(s), the reference voltage should still be available. Note that the CT & VT connections should be made as shown in the appropriate application diagram. The directional element analyses the relation between operating current and reference voltage, to determine the fault direction. This is related to the relay characteristic angle (range 15 to 83 ) as selected by the user. Typically a relay characteristic angle of 45 is chosen for transformer feeders and 30 for plain feeders as shown in Figure This relates to a system characteristic angle of 45º or 60º respectively, due to the internal quadrature connection. V 1 V 1 No trip Region No trip Region V31 45 V 12 Trip zone 45 lead through 135 lag V ' 23 V V 12 Trip zone 30 lead through 150 lag V ' 23 V 3 V V 2 23 V 3 V V 2 23 System characteristic angle 45, generally used for transformer feeders, or feeders "earthed" in front of the relay System characteristic angle 60 generally used for plain feeders, "earthed" behind the relay Fig Trip / No Trip region for directional element in the MRI (phase overcurrent) The trip zone indicated by Figure illustrates the operation for phase current I1 related to both the phase voltage V1, and the directionalising element from voltage V23. The operate zone is effectively bounded ±90 about the system characteristic angle for current levels exceeding the set level, as detailed in and The use of an efficient directional algorithm and high sensitivity voltage measurement, enables accurate assessment of the phase angle, even for close three phase faults. In order to prevent incorrect assessment, four consecutive direction measurements must occur before a trip operation can be allowed. The different time delays or time multipliers for forward and reverse direction, as detailed in & 6.3.5, enables the user to achieve a high degree of system grading. 20/7/99 Page 14 Issue 1

19 5.5. Earth fault directional feature (optional). Within the MRI range, two versions of earth fault protection are available; for application to: Isolated or compensated earthed networks (5.5.1) Solid or resistance earthed networks (5.5.2) This selection must be made at the time of order Earth fault direction feature for isolated or compensated earthed networks Isolated Systems. In an isolated system, although there is no direct connection between the system and earth, the capacitance of cables and other equipment can effectively tie the system to earth. In the event of a fault to earth, the disturbance causes a small capacitive current to flow which may be detected and acted upon by the relay. This residual current may be obtained by a Holmgreen connection of the line CT's. However, to produce the required accuracy of measurement, a core balance CT should, in almost all cases, be used. In order to determine the fault direction a voltage reference is required. Usually, this is obtained through the use of an additional broken delta winding on the Voltage Transformer. However, the MRI range eliminates the need for this additional winding by forming the residual reference voltage internally, from the three applied phase voltages. If this facility is employed, the applied voltages must be obtained from either a 5 limb VT or 3 single phase VT's, and the measuring method (6.3.13) should be set to "3PHA". Where a broken delta winding is used, as shown in Figure (a), the measuring method (6.3.13) should be set to "E-N". Where a line VT is not available it is possible to use a secondary winding on the system earthing transformer, as shown in Figures (b) & (c), and the measuring method (6.3.13) should be set to "1:1" MRI 14 a) Use of broken delta VT b) Use of earthing transformer MRI G MRI c) Use of generator/transformer earthing VT Figure /7/99 Page 15 Issue 1

20 Since the relay must determine the fault direction by evaluating a capacitive current, a SINE function is employed. i.e; A faulted line produces a 90 lagging current, whilst, a non-faulted line would reflect a 90 leading current. V e Reflected Fault Current (Non-faulted Line) Trip Region (Sin) I e (Faulted Line) Figure Trip / No Trip region for earth fault in an isolated system (SIN selection). The trip zone indicated by Figure illustrates the operation for the earth fault current Ie related to the residual voltage Ve, for an isolated system. The operate zone is determined by analysis of the capacitive component of the fault current for magnitudes exceeding the set level, as outlined in & /7/99 Page 16 Issue 1

21 Compensated System. In a compensated earthed network the system is connected to earth via a reactance, matched to balance the system capacitance. In the event of a fault to earth, the change in the balance of capacitive current, between the phases, is compensated by the neutral earthing reactance. Under these circumstances the relay must determine the direction of the fault by evaluating the resistive current by using a COSINE function. The residual current and voltage references are obtained as for an isolated system. V e Reflected Fault Current (Non-faulted Line) I e (Faulted Line) Trip Region (Cos) Figure Trip/No Trip region for earth fault in a compensated system (COS selection). The trip zone indicated by Figure illustrates the operation for the earth fault current Ie related to the residual voltage Ve, for an compensated system. The operate zone is determined by analysis of the resistive component of the fault current for magnitudes exceeding the set level, as outlined in & /7/99 Page 17 Issue 1

22 Earth fault direction feature for solidly connected or resistive earthed networks. The residual current may be obtained by a Holmgreen connection of the line CT's. However, a core balance CT may be used for improved accuracy. In order to determine the fault direction a voltage reference is required. Usually, this is obtained through the use of an additional broken delta winding on the Voltage Transformer. However, the MRI range eliminates the need for this additional winding by forming the residual reference voltage internally, from the three applied phase voltages. If this facility is employed, the applied voltages must be obtained from either a 5 limb VT or 3 single phase VT's. Alternatively a broken delta winding may be used, as shown in Figure (a) Solidly Earthed System. In a solidly earthed system, the fault current will lag the remaining phase voltage Vr by approximately 70. However, the internally formed reference voltage Ve "seen" by the relay, will be approximately 180 to the remaining phase voltage. Thus the relay has a characteristic phase angle of -110, as shown in Figure (Soli). V r -110 Trip Region (Soli) V e Relay characteristic angle -110, relay selected for solid earthed system. Figure Trip/No Trip region for earth fault in a solid system. The operate zone is effectively bounded ±90 about the relay characteristic angle for current levels exceeding the set level, as detailed in and /7/99 Page 18 Issue 1

23 Resistive Earthed System. In a resistive earthed system, the fault current will be approximately in phase with the residual voltage Vr. As with a solidly earthed system, the internally formed reference voltage Ve "seen" by the relay, will be approximately 180 to the voltage. Thus the relay has a characteristic phase angle of 170, as shown in Figure (Resi). V r Trip Region (Resi) 170 V e Relay characteristic angle 170, relay selected for resistance earthed system. Figure Trip/No Trip region for earth fault in a resistive earthed system. 20/7/99 Page 19 Issue 1

24 5.6. Requirements for the main Current Transformers. In order to ensure the correct operation of the MRI range of relays, protection class CT's must be utilised. Instrument CT's are NOT a suitable alternative. CT's should be chosen such that saturation, or loss of accuracy does not occur within the settings and operation ranges of the relays. In the absence of known settings the following may be regarded as an approximate guide. Line CTs For 1A secondary CT class 5P20 or 10P20 2.5VA (Allowing for up to 1Ω of secondary lead resistance) For 5A secondary CT class 5P20 or 10P20 5VA (Allowing for up to 0.5Ω of secondary lead resistance) Core Balance CTs For solid and resistive earthed systems CT Class 1.0/5P5, 2.5VA For isolated/compensated systems where sensitive settings are required. Special Core Balance CT Type Z, ratio 200mA/1.5mA for use with MRI-EX rated 1A. Stabilising Resistor. In the case where the earth fault input is supplied from the Holmgreen (residual) connection of 3 line CT's it may be necessary to fit an external stabilising resistor. Guildence on selecting a suitable resistor is given in Publication ref MR901. NOTE. with due regard to a suitable CT ratio and fault level capacity Blocking Input. By applying a voltage within the auxiliary voltage operating range to terminals ( terminal 54 is common to the RESET input ) the protection functions chosen by the user is blocked whilst the voltage is applied, (see section ) Reset Input. By applying a voltage within the auxiliary voltage operating range to terminals ( terminal 54 is common to the BLOCKING input ) all output relays may be reset. 20/7/99 Page 20 Issue 1

25 5.9. Reset Delay & Dwell Time. In order to provide better discrimination with Electromechanical relays two additional settings are provided Reset Delay. The reset delay delays the reset of the relay following a Flashing Fault (sometimes known as a Pecking Fault) which simulates the time an electromechanical relay takes in order to wind back a partially rotated Disk (IDMT). This may be selected as 0 or 60 seconds Dwell Time. The dwell time, is an additional delay introduced on the output contacts used to prevent the contacts opening during a tripping action. This may be selected as 0 or 200 ms Circuit Breaker Failure Protection (t CBFP ). The CB Failure Protection is based on supervision of phase currents during tripping events. This protective function becomes active only after tripping. The test criterion is whether all phase curents have dropped to <1% x In within t CBFP (Circuit Breaker Failure Protection adjustable between s) If one or more of the phase currents have not dropped to <1%xIn within this time, CB failure is detected and the assigned output relay is activated. The CB failure protection function is deactivated again as soon as all the phase currents have dropped to <1%xIn within t CBFP Display of Pick-up event. If after a pick-up (starting) the existing current drops again below the pickup value, e.g. I>, without a trip being initiated, LED I> signals that an activation has occurred by flashing fast. The LED keeps falshing until it is reset again (push button <SELECT/RESET>). Flashing can be suppressed when the parameter is set to NOFL. This applies also to the I>>, IE>, IE>> functions Display of Measuring values as primary quantities (I prim phase). With this parameter it is possible to show the indication as a primary measured value. For this purpose the parameter must be set to be equal with the rated primary CT current. If the parameter is set to "SEK" the measuring value is shown as a multiple of the rated secondary current. Example: The current transformer used is 1500/5A. The primary current is 1380A. The paramter is set to 1500A and on the display "1380 A" is shown. If the parameter is set to "SEK" the value shown on the display is "0.92"xIn. Note. The pick-up value is set to a multiple of the rated secondary CT current. 20/7/99 Page 21 Issue 1

26 5.13. Display of Earth Current As Primary Quantity (I prim earth). The parameter of this function is to be set in the same way as that described under Section If the parameter is not set to "SEK" then the measuring value is shown as primary current in amperes (this applies to MRI-IEX, MRI-IEK and MRI-EX as well). Apart from that the indication refers to % of In Display of Residual Voltage UE as Primary Quantity (U prim /U sec ). The residual voltage can be shown as primary measured value. For this parameter the transformation ratio of the VT has to be set accordingly. If the parameter is set to "SEK", the measuring value is shown as rated secondary voltage. Example. The voltage transformer used is 10kV/100V. The transformation ratio is 100 and this value has to be set accordingly. If rated secondary voltage should be shown, the parameter is to be set to 1. 20/7/99 Page 22 Issue 1

27 6. Operation and setting 6.1. Layout of the control elements. All control elements required for the operation and adjustment of the MRI are located on the front panel. They are divided according to function into the three following groups: Alphanumeric Display: Indication of parameter set values, actual measured values and recorded fault data. LED's: Indication of selected parameters and measured quantities. Push Buttons: Selection of parameter to be adjusted, quantity to be measured and adjustment of parameter values. Where; <SELECT / RESET> <UP> <DOWN> <ENTER> <TRIP> Selection of the parameter to be set and the relay quantities to be measured. Continuous pressing as the reset function. Increment of the setting values for the parameter selected. Decrement of the setting values for the parameter selected. Storage of the setting values for the selected parameter. Testing of the output relay circuits Relay setting principles. Up to ten basic relay parameters may be set by the user, dependent upon relay type; Phase overcurrent: I> CHAR I> ti> I>> ti>> Starting current for phase overcurrent Time current characteristic for phase overcurrent Tripping time delay for definite time overcurrent or time multiplier for inverse time overcurrent Current setting for high set overcurrent Tripping time delay for high set overcurrent Earth Fault: (optional) IE> CHAR IE tie> IE>> tie>> Starting current for earth fault Time current characteristic for earth fault Tripping time delay for definite time earth fault or time multiplier for inverse time earth fault Current setting for high set earth fault Tripping time delay for high set earth fault By pressing the <SELECT/RESET> push button, the parameter to be modified is reached. The corresponding LED illuminates on the curve and the present set value of the selected parameter is indicated on the display. This set value may then be increased or decreased by pressing the <UP> or <DOWN> buttons respectively. The selected set value is only stored after pressing the <ENTER> push button and inputting the correct password. This means that adjustment of the unit is only possible by authorised users. 20/7/99 Page 23 Issue 1

28 Password protected parameter adjustment. The adjustment of all relay settings are password protected, however, to enable ease of adjustment, for authorised users, application of the password is usually only required once for multiple parameter adjustment. The following step by step sequence is given to illustrate the implementation of the password protection facility, where a new relay setting is to be applied: After the present setting value has been selected and changed using the <UP>, <DOWN> push buttons, the <ENTER> push button should be pressed. The message "SAV?" appears on the display, to confirm that the new setting value is to be saved. After pressing <ENTER> again, the password will be requested. The message "PSW?" is displayed. After the password has been given correctly, as indicated by the message "SAV!", the new setting value may be stored by pressing the <ENTER> push button for at least 3 seconds. The new setting parameter then reappears on the display. A password consists of four push button operations. The pressed push buttons and their sequence define the password. If the four push buttons are defined by the following symbols: <SELECT/RESET> = S <DOWN> = <UP> = <ENTER> = E Then a password " E S" is achieved by the following sequence: <DOWN> <ENTER> <UP> <SELECT/RESET>. After a password is given correctly, parameter setting is permitted for five minutes. Subsequent parameter setting made within the five minute period after the password was inputted, does not require renewed password entry. Furthermore, the valid period for parameter setting is automatically extended for a further 5 minutes after each push button operation. If no push button is pressed within the 5 minute period then the validity of the password will be suspended. To enter further parameters after this period re-application of the password is required. During the 5 minute period when changes may be made, a new set value, acknowledged by "SAV?" then "SAV!", may be stored by pressing <ENTER> for approximately 3 seconds. 20/7/99 Page 24 Issue 1

29 6.3. Setting procedure. The following sections describe in detail the setting of all relay parameters. Some sections are only applicable to the more comprehensive devices, eg earth or directional elements Starting current for phase overcurrent relay (I>). The displayed setting value for this parameter is related to the nominal rated current (IN) of the relay. Thus; Starting current (IS) = Displayed Value x Rated Current (IN) e.g. If Displayed Value = 1.25, then IS = 1.25 x IN Time current Characteristic for phase overcurrent relay (CHAR I>). By setting this parameter, one of the following four options is displayed: DEFT NINV VINV EINV RINV LINV - Definite Time - Normal Inverse - Very Inverse - Extremely Inverse - RI Inverse - Long Time Inverse Any one of these six characteristics can be chosen by using the <UP> <DOWN> keys and can be stored by pressing <ENTER>. For more details on the characteristic curves see Section Tripping time delay or time multiplier for phase overcurrent relay (ti>). After the time/current characteristic has been selected, the time delay (or time multiplier) should be changed accordingly. In order to avoid an unsuitable arrangement of relay modes the following precautions are taken: Adjustment of the time delay setting is automatically prompted for after a change in the set time/current characteristic. LED ti> flashes yellow to remind the operator to change the time delay setting accordingly. After pressing the <SELECT/RESET> push button, the present time delay setting value is shown on the display. A new setting value may then be entered. If the relay characteristic has been changed (e.g. from DEFT to NINV), but the time delay setting has not, the relay will, after 5 minutes, automatically set itself to the most sensitive time setting value available for that selected characteristic. The most sensitive time setting value implies the fastest tripping for the selected relay characteristic. If the time delay or the time multiplier is set out of range, "EXIT" appears on the display, and the low set stage of the relay is blocked. 20/7/99 Page 25 Issue 1

30 Where the MRI is fitted with a directional element, the different tripping time delays or time multipliers may be chosen for both forward and reverse faults. When setting the tripping time delay, the set value for forward faults appears on the display first and the LED under the "arrows" illuminates GREEN. The set value may be changed with the <UP> and <DOWN> push buttons, and then stored. By pressing the <SELECT/RESET> button the tripping time delay for reverse faults appears on the display and indicator changes from GREEN to RED. If the time delays are set equally for both forward and reverse faults, the relay trips in both cases with the same time delay, effectively nullifying the directional feature. If the time delay for reverse faults is set out of range, "EXIT" on the display, the relay is blocked for reverse faults. The low set stage of the overcurrent relay may also be blocked via terminals 54 and 55 (see Section ). It is also possible to inhibit the alarm relay for a fault in the reverse direction. The display shows either "NOWA" - No alarm when a fault occurs in the reverse direction, or "WBAK" - Alarm relay is activated when a fault occurs in the reverse direction. During this procedure the LED is illuminated RED Current setting for high set stage of phase overcurrent relay (I>>). The current setting value of this parameter is related to the nominal rated current of the relay. Thus; I>> = Displayed Value x Rated Current (IN) e.g. If Displayed Value = 20, then I>> = 20 x IN The high set stage of the overcurrent relay is blocked if the setting value is set to "EXIT". The high set stage may also be blocked via terminals 54/55, see Section Tripping time delay for high set stage of phase overcurrent relay (ti>>). Independent from the chosen tripping characteristic for I>, the high set stage I>> always has a definite time tripping characteristic. An trip delay value in seconds appears on the display. The setting procedure for forward or reverse faults described in paragraph is also valid for the tripping time of the high set stage Starting current for earth fault relay (IE>). (Similar to 6.3.1) Time Current characteristic for earth fault relay (CHAR IE). (Similar to 6.3.2) Tripping time delay or time multiplier for earth fault relay (tie>). (Similar to 6.3.3) 20/7/99 Page 26 Issue 1

31 Current setting for high set stage of earth fault relay (IE>>). (Similar to 6.3.4) Tripping time delay for high set stage of earth fault relay (tie>>). (Similar to 6.3.5) Earthing type COS/SIN Measurement. Where an isolated or compensated earthed system version of the relay is supplied, the directional element for earth faults must be set to SIN or COS as appropriate. Please refer to Section for more details SOLI/RES Setting. Where a solid or resistive earthed system version of the relay is supplied, the directional element for earth faults must be set to SOLI or RESI as appropriate. Please refer to Section for more details Residual Earth Fault Voltage (VE). Operation of the earth fault (directional) element is inhibited for residual voltage below this preset value, (isolated earth system) Residual Earth Fault Voltage Measurement Method. The measuring method must be set to "3PHA", "E-N" or "1:1" as required. (5.5.1, isolated earth system) Earth Fault Response. The response to earth faults may be selected to "TRIP" or "WARN", ie to allow an alarm without causing a trip function, (isolated earth system) Nominal frequency. The FFT Algorithm employed requires the nominal frequency as a parameter for correct digital filtering of the input currents. By pressing <SELECT> the display shows "f=50" or "f=60". The desired nominal frequency may then be selected and stored. 20/7/99 Page 27 Issue 1

32 Assignments Of The Blocking Inputs. The blocking input of the MRI relays can be programmed so that the blocking input will only block certain functions. The blocking inputs are found at the beginning of assignment mode. By pressing push buttons <ENTER> and <TRIP> simultaneously, the assignment mode is selected. The first function that can be blocked has its LED light up and the display shows whether it is blocked or not. To switch the blocking on (display shows BLOC) or off (NOBL) press the <VALUE UP> or <VALUE DOWN> buttons and then save the parameter. The following functions can be blocked. Low Set Overcurrent High Set Overcurrent Low Set Earth Fault Overcurrent High Set Earth Fault Overcurrent The assignment mode can be terminated at any time by pressing the <SELECT/RESET> push button for approximately 3 seconds Blocking Of Protection Functions. The blocking function of the MRI can be set according to requirement. By applying the auxiliary voltage to 55 and 56, the functions chosen by the user can be blocked. Setting of the parameter should be done as follows: 1.) When pressing push buttons <ENTER> and <TRIP> at the same time the message "BLOK" is displayed (i.e. the respective function is blocked) or "NO_B" (i.e. the respective function is not blocked). The LED allocated to the first protection function I> is illuminated. 2.) By pressing push buttons <VALUE UP> and <VALUE DOWN> the value displayed can be changed. 3.) The changed value is stored by pressing <ENTER> and entering the password. 4.) By pressing the <SELECT/RESET> push button, any further protection function which can be blocked is displayed. 5.) Thereafter the blocking menu is left by pressing <SELECT/RESET> again. Function Display LED/Colour I> Overcurrent (Low Set) NO_B I> yellow I>> Overcurrent (High Set) BLOC I>> yellow IE> Earth Current (1 element) NO_B IE> yellow IE>> Earth Current (2 element) NO_B IE>> yellow tcbfp Switch Failure Protection NO_B CB green Table Default settings of both parameter sets. 20/7/99 Page 28 Issue 1