RCS-978A Transformer protection equipment
RCS-978 Transformer Protection
Application
RCS-978 is a series of following micro-processor based transformer protection equipments:
- RCS-978A is applicable to three-winding transformers of 500 kV. Five branches' currents could be conducted to its differential circuit.
- RCS-978B is applicable to autotransformers of 500 kV with one and half circuit breakers connection on high voltage side and two branches on low voltage side. Five branches' currents could be conducted to its differential circuit.
- RCS-978C is applicable to autotransformers of 500 kV with one and half circuit breakers connection on high and medium voltage sides both. Five branches' currents could be conducted to its differential circuit
- RCS-978D is applicable to autotransformers of 330 kV. Five branches' currents could be conducted to its differential circuit.
- RCS-978E is applicable to various transformers of 220 kV. Four branches' currents could be conducted to its differential circuit.
- RCS-978F is applicable to three-winding transformers of 220 kV. Five branches' currents could be conducted to its differential circuit.
General
RCS-978 series of transformer protection based on principle of duplicated main and back-up protection. All of the electric quantities protection of a main transformer are integrated in these equipments. The main protection covers those of steady state percentage differential, unrestraint differential, high sensitive DPFC percentage differential, zero sequence percentage differential or differential per side (for autotransformer) and overexcitation protection (definite or inverse time optional ), etc.. The back-up protection covers those of impedance, directional overcurrent with composite voltage blocking, zero sequence overcurrent, zero sequence overvoltage, "gap" zero sequence overcurrent*, overload alarm, air cooling initiation, on-load voltage regulation with overload blocking, zero sequence alarm, TA and TV abnormal alarm, etc. Besides, additional function of RCS-978 includes perfect event message processing, flexible communication interfaces, fault recording compatible with COMTRADE, software of management and fault analysis, etc.. Following table lists protection functions of various types of these equipments.
Protection functions
| Protection functions |
978A |
978B |
978C |
978D |
978E |
978F |
| DPFC differntial |
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| Steady state percentage differential |
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| Unrestraint differential |
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| Zero-sequence differential or differential per side |
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| Overexcitation |
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| Impedance |
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| Overcurrent with composite voltage blocking |
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| Zero sequence directional overcurrent |
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| Zero sequence overvoltage |
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| "Gap" zero sequence overcurrent and overvoltage* |
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| Voltage regulation with overload blocking |
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| Overload alarm |
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| Air cooling initiation |
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* "Gap" means neutral point of the transformer being grounded through gap.
Features
- Sampling rate is as high as 24 points per cycle. Full-wave Fourier algorithm is used for principle relays. Parallel real-time calculation is used for all main and back-up relays during fault conditions even in such high sampling rate. Reliability and speed of the equipment could be enhanced then.
- Independent general starter is equipped in the management module of the equipment. Its operation closes positive power source of the output circuit. Different starters are also utilized for various relays. Trip signal could be sent out from a relay only when its starter in CPU module and corresponding starter in management module operate simultaneously. Security could be very high then.
- Phase difference and balance factors of current of each side could be configured by software. Setting range of balance factor of phase current could be up to 16 times.
-->Ytransformation is used for balance of differential current and inrush or fault current could be distinguished correctly. So operation could be speeded up.
- Characteristic of steady state protection consists of three broken-lines. Differential current's second and third harmonics or waveform are used for inrush blocking while its fifth harmonic for overexcitation blocking. Harmonics are used for identification of TA saturation and mal-operation of steady state percentage differential protection during external fault accompanying TA saturation could be avoided then.
- Many blocking criteria are adopted for security. Such as second and third harmonics of differential current for inrush blocking, fifth harmonics of differential current for over- excitation blocking, second and third harmonics of phase current for saturation of current transformer blocking, etc.
- DPFC of differential current represents only change of differential and restraint currents. It is sensitive to small current fault within the transformer and regardless of the load current. Its performance against current transformer saturation is also good because of high settings of its restraint factor and restraint current.
- Zero sequence current percentage differential protection is adopted for autotransformer. Zero sequence currents of each side are got from the equipment. Their balance could be adjusted by software. Positive current restraint and criterion of saturation of TA are combined to avoid mal-operation of this protection.
- Distinguish of open and short circuit of current transformer is more reliable because of combination of voltage and current value method adopted.
- Characteristic of inverse time overexcitation protection could coordinate with overexcitation curves of different kinds of transformers. Multiple of excitation measured could reflect actual condition of the transformer more exactly.
- Maximum requirement to back-up protection of all sides of the transformer is considered. The tripping output circuit could be configured by tripping matrix and suitable to any mode of tripping. The impedance protection equips with swing blocking function and could be disabled during TV failure. Zero sequence overcurrent protection adopts harmonics restraint blocking to prevent influence of sympathetic inrush.
- Friendly man-machine interface is used. Connection of the transformer, voltage and current on each side, power frequency, multiple of overexcitation, direction of the current and differential current as well as the time could be displayed on LED. Operation of the keypad is easy to be handled. Simplified Chinese characters are used for menu and report printed.
- PC software packet and communication facilities make configuration and supervision more easily. Status and information of the equipment such as settings, real-time analogue quantities and status inputs as well as information recorded could be read remotely. Fault analysis could be made conveniently by software packet.
- The equipment uses an integral front panel and closed cabinet of height 8U. Strong and weak currents are divided strictly. Traditional method of connections on the rear is not adopted. Immunity measures are also taken for the software. Therefore, immunity performance of the equipment is so enhanced that it could pass EMC tests of lots of standards smoothly.
Technical data
| Ratings DC control voltage 220 V, 110 V Tolerance -20% - +15% AC voltage 100 V /  3AC current 5 A, 1 A Frequency 50 Hz |
Setting range (cont'd) Second harmonics restraint factor 0.1 - 0.35 Third harmonics restraint factor 0.1 - 0.35 Differential current for current transformer alarm 0.1 - 1 Ie Restraint factor for zero sequence current percentage differential protection 0.3 -0.75 Current setting for back-up protection 0.5 - 150 A (In = 5 A ) 0.1 - 30 A (In = 1 A ) Impedance setting for back-up protection 0.1 - 100  Voltage setting for back-up protection 2 - 100 V Zero sequence voltage setting for back-up protection 2 - 150 V Factor setting of overexcitation protection 1.0 - 1.5 Time setting of overexcitation protection 0.1 - 6000 s Zero sequence voltage setting in "gap"case * 10 - 220 V Zero sequence current setting in "gap"case * 0.5 - 150 A (In = 5 A ) 0.1 - 30 A (In = 1 A ) Directional unit polarized positive sequence voltage, start per phase |
| Power consumption AC current circuit at rated current < 1 VA /  ( In = 5 A)< 0.5 VA / ( In = 1 A)AC voltage circuit at rated voltage < 0.5 VA / DC control circuit quiescent 50 W energized 70 W | |
| Operation time Unrestraint differential protection  15 ms(1.5 setting value)Steady state percentage differential protection 30 ms (2setting value)DPFC percentage differential protection 30 ms (2setting value)Zero sequence percentage differential protection 30 ms (2setting value) | |
| Pick-up range of starter Steady state percentage differential starter 0.2 - 1.5 Ie DPFC percentage differential starter 0.2 Ie Zero sequence percentage differential starter 0.1 - 1.5 In Back-up phase current starter 0.5 - 20 A (In = 5 A) 0.1 - 4 A (In = 1 A) Back-up zero sequence current starter 0.5 - 20 A (In = 5 A) 0.1 - 4 A (In = 1 A) Back-up DPFC phase-to-phase current starter 0.2 Ie Back-up zero sequence current starter in "gap" case * 0.5 - 20 A (In = 5 A) 0.1 - 4 A (In = 1 A) back-up zero sequence overvoltage starter in "gap" case * 10 - 220 V | |
| Tolerance of settings Current  5% Voltage 5% Impedance 5% Time 3% of setting +40 msOverexcitation factor 1% Harmonic restraint factor 5% DPFC current 15%Limit of operation range of directional unit 3 | |
| Setting range Unrestraint differential protection 2 - 14 Ie Restraint factor of steady state percentage protection 0.2 - 0.75 |
Communication Port 2 RS-485,optic fiber interface is available 2 RS-485, for printer and PCProtocol IEC 60870-5-103 |
* "Gap" means the neutral point being grounded through gap (for RCS-978E only).
| Capacity of output contact DC 5 A for making |
EMC test (cont'd) Power frequency magnetic field IEC 61000-4-8, class 4 Pulse magnetic field IEC 61000-4-9, class 3 |
| EMC test 1 MHz bursts disturbance IEC 60255-22-1, class III Electrostatic discharge IEC 60255-22-2, class III Radiated electromagnetic field IEC 60255-22-3, class III Fast transient disturbance IEC 60255-22-4, class IV Surge IEC 61000-4-5, class 4 Conducted disturbance induced by radio- frequency field IEC 61000-4-6, class 3 | |
| Ambient temperature Normal operation -5  - 40 Extreme range - 10 - 55 Storage and transportation - 25 - 70 | |
| Shelf Dimensions width 487 mm (19") height 353 mm (8U) depth 285 mm |