Earth fault protection for isolated neutral systems with frequency converters

Transcription

1 Earth fault protection for isolated neutral systems with frequency converters Page Issued June 999 Changed since July 998 Data subject to change without notice (SE97089) Features Earth fault and flash-over functions in the same relay package Operates for earth fault resistances less than 5 kohm Operates for flash-overs in the source transformer Operation not affected by harmonics or capacitances to earth Can be connected either to the neutral point of the system or to the phases Two variants; one for system voltages within V and one for V Trip relay included Flag for indicating flash-over operation Test switch included Application is used for supervision of isolated neutral. operates for earth faults within the entire regulated frequency range. Not even the high harmonics, caused by the frequency converter and which are capacitively earthed, affect the operation of. The harmonics are especially high when the frequency converter is pulse-width-modulated (PWM). Conventional earth fault relays that measure the neutral point voltage are therefore not suitable for use on such systems. Operation is obtained, after 5-0 seconds, when the resistance to earth measures 5 kohm or lower. Filter-circuits are used to attenuate the influence of the ac voltages and capacitances to earth M M The will cope the conditions typically found on systems having PWM frequency converters. The relay can also be applied on systems with ac/dc-converters and low frequency induction stirrers. For earth fault operation injects a dc voltage onto the system and then measures the direct current which arises during earth faults. Neutral point equipment earth fault/flash-over relay Frequency PWM converter Ac/dc converter Fig. Principle application of < (96000)

2 Page Application (cont d) The flash-over protection operates in less than 00 ms for a flash-over between the primary and secondary side of the source transformer. For application on systems without an available neutral point, is connected to the phases via supervised fuses. To systems with a neutral point available, is connected via neutral point equipment. For connection to a system with a neutral point either variant can be used along with the neutral point equipment. If variant is used the three inputs should, in this case, be connected in parallel. For connection to the phases in a system without a neutral point the variant for V is used. Each phase should be connected to a fuse mounted less than 0,5 m from the connection point. The fuses may be omitted if is mounted closer than 0,5 m to the connection point or if the housing for the wire is fireproof. The neutral point equipment has a voltage dependent resistor connected in series with a spark-gap. If a flash-over occurs in the transformer, the resistor limits the voltage to approx. 000 V, provided the supplying system limits the current to 5 A. When an earth fault occurs the injected current flows entirely through the earth fault. The spark-gap prevents current flow via the voltage dependent resistor to earth, thus avoiding incorrect earth fault current measuring. The neutral-point equipment also contains a resettable fuse and a resistor. The resistor limits the fault current to values which the fuse is capable of interrupting. To reduce humidity, a radiator with a thermostat is included. Fig. Fig. < Principle connection of, variant and Principle connection of, variant < (960006) M (960005)

3 Page Design Two variants of the relay are available. Variant is intended for system voltages between 80 and 500 V. Variant is intended for system voltages between 80 and 660 V. consists of a supply unit, XTE, a measuring unit, XNAF, and an XMA medium-duty output relay with two changeover contacts and an XME 8 heavy-duty output relay with a red flag and two make contacts. The SMA operates for earth faults and the XME 8 operates for and indicates flash-over. has different terminals for auxiliary voltages 0-0 V and 0-0 V. The auxiliary voltage is transformed and rectified into two voltages; one for injecting a dc voltage to the network and one for supplying a voltage to the measuring circuit. Both voltages are stabilized and input resistors provide the relay with a constant and high input impedance. A level detector with a fixed operate value is used for earth faults and an adjustable level detector for flash-over. Variant is a 0C assembly and has a test switch. Variant is without the test switch and assembled on an insulating plate. Power resistors are included to provide an artificial neutral point. (SE85) Fig. variant

4 Page Technical data ated voltage, r variant variant Operate value: Earth fault, < Flash-over, > Graduation error (% of highest setting) < % eset ratio: Earth fault Flash-over Operate time: Earth fault Flash-over Indicator at flash-over Permitted earth leakage capacitance Overload capacity Continuously s Overload capacity for the neutral point equipment Input impedance Permitted ambient temperature Auxiliary voltage V, Hz V, Hz 5-0 kohm at ac (0,5-50 Hz) 5-0 kohm at dc, fixed value ) V, Hz adjustable < 00% > 70% 5-0 s 70 ms at set value Flag 0 µf/phase 550/000 V, variant 750/5000 V, variant 5 A during 0,5 s 5 kohm resistive -0 to +55 C 0-0/0-0 V Hz, reconnectable Permitted auxiliary voltage deviation -0% to +0% Power consumption in auxiliary voltage circuit Dimension/weight: variant variant Insulation tests: Dielectric tests variant variant Impulse voltage test Disturbance tests: Power frequency test Fast transient test MHz burst test Interruptions in auxiliary voltage Contact data <0 VA 0C/,6 kg Height 0 mm Width 8 mm/8 kg 50 Hz,,0 kv, min 50 Hz, 5,0 kv, min,/50 µs, 5,0 kv, 0,5 J 50 Hz, 0,5 kv, min -8 kv, min,5 kv, s -500 ms operation is not interrupted at interruptions in auxiliary voltage <00 ms see MK BEN (XMA and XME) ) The operate value is influenced by the earth fault dc potential to earth according to the formula: 0 + FN , 8 5 [kohm] where: = The operate value FN = The dc voltage between the fault point and the neutral point

5 Page 5 Diagrams 0C 5) AA 0 9A 5 S A ) ) ) ) 0 7A 5:7 5:5 r 0 TXP 8 07 XTE 9 XNAF H 5 XMA 5 XME 8 0 A A A 8A 07:5 07: 07: =0-0V, 50-60Hz =0-0V, 50-60Hz 0V ) TIP, FLASH-OVE ) TIP, EATH FALT ) ALAM, FLASH-OVE ) ALAM, EATH FALT 5) NETAL POINT EQIPMENT Fig. 5 Terminal diagram No AAA, variant ø9( x ) X K 7 06-DA 9:5 9:7 9:5 9:7 X 9:6 9:6 9:6 9: X : 0:5 0:5 0: 0: = Hz 0-0 V = Hz 0-0 V 0 X ) L() L(S) L(T) ) CONNECTION WIES WITH 5 kv DIELECTIC TEST VOLTAGE K 6 8 K -7 X X,X ESISTO TEMINAL TXG 8- X X,X oo oo 78 ø7( x ) Fig. 6 Circuit diagram No AA, variant

6 Page 6 Ordering Specify: Quantity Ordering No. - K AB, variant - K AB, variant - SA 00-A, neutral point equipment (to be ordered from ABB Distribution) Desired wording on the lower half of the test switch face plate max. lines with characters per line. Mounting:, variant is provided on 0C apparatus bars. When additional mounting is required specify a equipment frame for 9 rack mounting or type HGX case for panel mounting., variant is provided on an insulating plate for panel mounting or cubicle mounting. See under Case dimensions and mounting instructions. Sample specification Earth fault/flash-over relay with or without neutral point equipment. The relay shall operate after 5-0 seconds for an earth fault, reset ratio shall be < 00%. It shall operate in less than 00 ms for a flash-over, reset ratio shall be > 70%. It shall be unaffected by main frequency-, converter-, and harmonic voltages transferred to the relay via system capacitance to earth. Two output relays, one for earth fault and one for flash-over operation shall be included. The relay shall be suitable for 9 rack mounting and provided with a test-switch for secondary injection testing. eferences Auxiliary relay, XMA Auxiliary relay, XME 8 Test system COMBITEST Dimensions Description MK BEN MK BEN MK 5 00-BEN MK 5 00-BEN K E Manufacturer ABB Automation Products AB Substation Automation Division SE-7 59 Västerås Sweden Tel: +6 (0) 0 00 Fax: +6 (0) 69 8