Chapter 5-2-10 Protection of Underground Cable Lines
Article 497. Relay Components for Underground Cables
As stipulated in Technical Regulation.
Article 498. Protection against Earth Faults for Underground Cable Lines
If underground cables have high capacitance to the ground, the malfunction of protective relays due to the transient oscillation current of the cable may happen in case of external faults of protective areas. Therefore, it is desirable to consider the following.
-Install the compensating reactor for the cable near the target cables.
-Tripping the circuit breaker after transient oscillation current decreases
- If the active current of the fault current is smaller than the charging current of the cable, it is desirable to install neutral grounding resisters at the both ends of the cable, to increase the active current of the fault current.
Chapter 5-3 Control Systems
Chapter 5-3-1 Control equipment and Auto-reclosers
Article 499. Functions of Automation and Remote Control
As stipulated in Article 499 in Technical RegulationVol.1.
In power system and electrical equipment which can be installed with auto-control devices, even if the auto-control devices do not obey the application scope of cthisapter but other regulations, the operation of such auto-control devices shall coordinate with operations of auto-control devices subject to requirements mentioned in this chapter.
In even customer’s power network, automatic devices arerecommended to be equipped in case that interruption of electric power supply due to trip by protective relays and autocontroldevices cannot be acceptable.
Article 500. Application Conditions of Auto reclosers
1.The following items should be considered in order to decide whether auto-recloser can be applied to overhead cable line with voltage up to 35kV or not.
(1)It should be checked whether auto-reclose affects cable line by switching operation of circuit breaker. (e.g. open arc at cable line where several transformers are connected)
(2)It should be checked whether protective relay for cable line can be calibrated to ensure selective trip in case of fault
Auto-recloser should not be applied to underground cable lineGenerally,. since most of the faults which occur at underground cable line are permanent fault, such faults cannot be extinguished by temporarily interrupting the fault part from power lineTherefore,. auto-reclose should be carried
out in case of fault at underground cable line.
2. Auto-reclose of bus-bar of a power plant or a substation shall obey either the following requirements.
(1) Automatic forced charging of bus-bar
Bus-bar is charged by operation voltage through one circuit breaker from one of the live power lines which are connected to the bus-bar.
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(2) Automatic restore of diagram
First, bus-bar is charged by operation voltage through one circuit breaker from one of the live power lines which are connected to the bus-bar. After this charging is completed, remaining power outage components are charged one by one. This type auto-recloser should be equipped at the substation without on-duty stuff.
For substation which has two stepdowntransformers operating independently, autorecloserfor bus-bar should be equipped at low voltagedesi or medium voltage side of transformer and in combination with auto-switching device. In case of fault inside the transformer, the auto-switching device interrupts the fault transformer and auto-recloser shall not operate.In case of other faults, auto-recloser interrupts the fault transformer.
For substation which has two stepdowntransformers operating in parallel on the bus-bar, autoswitching device can be added to auto-recloser if either one of the two transformers is in standby
mode.
3. Auto-reclose of transformers shall obey the following requirement
Auto-recloser should be equipped at substation which has one step-down transformer with capacity of more than 1MVA and circuit breaker for over-current protection at the power source side of the
transformer. If disconnection of the transformer causes power outage |
at consumers, the auto- |
recloser is allowed to operate in case that the transformer is disconnected due to operation of short |
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circuit protective relay attached to the circuit breaker at its power source side. |
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In addition to the above, it shall be confirmed that the protective |
relay for fault inside the |
transformer does not operate. |
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4.Auto-reclose of motors disconnected for self-start-up of key motors shall obey the requirement stipulated in Article 509.
Auto-recloser shall be equipped at bypass circuit breaker, busbar circuit breaker and section circuit breaker.
Article 501. Cases Auto recloser not be allowed to operate
If a circuit breaker is interrupted as soon as this circuit breaker is closed by auto-recloser or manual |
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operation, this circuit breaker shall not be reclosed because the electrical fault is considered to remain. |
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In case of electrical fault inside a transformer and a |
rotary machine such as generator, |
rotary |
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compensator and motor, autoreclose- |
is prohibited because |
such electrical fault is considered |
to |
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remain. For the same reason, in case ofelectrical fault in an underground cable, autoreclose- |
is |
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prohibited. |
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As for the loads shed from the power gird due to by frequency decrease, autoreclose- |
of such loads is |
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prohibited in order to avoid frequency decrease again. |
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Article 502. Operation Period Requirements
3-phase auto-recloser with 2time trips should be applied to overhead line, especially to single power line supplied with power from one side.
As for overhead power line with voltage up 35kV,to which is not equipped with standby power source, 3-phase auto-recloser with 2time trips should be applied to such power line preferentially.
In power grid with isolated neutral or neutral point grounded through compensator, the second time of auto-reclose should be locked in case that earth fault occurs (voltage at the neutral point increases
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excessively) after the first time of auto-recloser. The duration between the first time and second time of auto-reclose shall not be smaller than 20 seconds.
The duration between the first auto-reclose and the second auto-reclose shall be decided based on the circuit breaker operating sequence duty. Therefore, the performance of the circuit breaker shall satisfy the requirement on the auto-reclose.
Article 503. Operation Time Requirements
As for the power line supplied with power from both sides, operation time of-phase3 |
auto-recloser |
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shall be decided in consideration of ability to non-simultaneously interrupt two circuit breakers at the |
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both ends. In this case, the operation time of buckupprotective relay should not be considered.And |
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operation time of nonsimultaneous- |
interrupt of circuit breakers at the both |
ends |
by vertical |
differential protective relay shall not be considered. |
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In order to enable 3-phase auto-recloser to operate efficiently, the operation of thephase3- |
auto- |
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recloser can be delayed, if such delay of operation of 3-phase auto-recloser is acceptable. |
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If the both ends of a power line are still connected electrically in case that the power line is interrupted by protective relay, auto-recloser without synchronous check should be equipped at this power line.
Article 504. Required Application Conditions for Single Transmission Lines
The type and function of autoreclosershould be selected based no individual conditions of power system and electrical equipment.
Quick-act auto-recloser and 3-phase quick-act auto-recloser should be installed in power line in order to automatically reclose in case that the angle between electromotive force vectorstheofpower systems to be connected is small.-phase3 quick-act auto-recloser can be used if the requirements below are satisfied.
-The performance on opening and closing of circuit breaker meetsrequirements on quick-act autorecloser
-After re-energized, parallel power lines can operate synchronously and largest electromagnetic moment of synchronous generator or compensator is lower than electromagnetic moment in case that 3-phase short circuit occurs at the terminal of the synchronous generator or compensator..
The largest electromagnetic moment will be |
calculated based on the maximum allowable |
deviated angle between two electromotive force vectors of power systems at-phase3 quick-act |
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auto-reclosing. |
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When back-up protective relay operates, phase3- |
quick-act auto-recloser shall not operate. |
Moreover, when auto-switching device for the circuit breaker operates, -3phase quick-act autorecloser shall not operate or shall operate with timedelay- . In order to ensure the stability of the power system, 3-phase quick-act auto-recloser shall not be applied in case that the failure of operation of the 3-phase quick-act auto-recloser causes several interrupts by protective relays.
Asynchronous auto-recloser can be applied in the case following cases are satisfied..
(1) Electromagnetic moment of generator or synchronous compensator in case of asynchronous energizing is lower than electromagnetic moment in case that-phase3 short circuit occurs at output terminal of the generator or compensator. It should be checked whether asynchronous autorecloser can be applied or not by initial calculationresult of short circuit in case that the
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transformer is energized at angle of 180 degree.
(2) Maximum current which flows through transformer in case that the transformer is energized at
angle of 180 degree is lower than short circuit current at output terminal of the transformer |
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(3) Re-synchronization |
can |
be |
ensured after asynchronous autoreclose- . If |
asynchronous |
mode |
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continues for long |
time |
after |
asynchronous autoreclose,- |
countermeasures |
to prevent or |
break |
such asynchronous mode shall be taken.
When asynchronous auto-recloser is applied, measures to avoid its unnecessary trip shall be taken. For that purpose, the circuit breaker should be closed according to the designated order on autoreclosing.
Auto-recloser for auto-synchronization can be applied in power line to energize the power line in case that the phase displacement angle is allowed.
Auto-recloser can be operated in the following way.
First, either end of the power line shall be energized, and second,phase 3auto- -recloser with accelerator without check of line voltage, 3-phase auto-recloser with check of no-voltage on the line, or auto-recloser for auto-synchronization can be applied.Auto-recloser for auto-synchronization can be applied under the condition that the other end of the power line is energized successfully.
In order to implement autosynchronization,- device to synchronize voltage, frequency and phase displacement on the line can be applied in case of unchanged angular displacement.
Auto-recloser should be arranged so that it can change the sequence for energizing circuit breakers at the two ends of the power line.
As for power linewith potential transformer to check voltage on the power line forphase3autorecloser, protective relay which operate by line voltage or phase voltage, negative and zero sequence voltage.
As for single power line supplied from two power supply sources connected to power systemwith small capacity power plants, 3-phase auto-recloser with automatic self-synchronization of hydraulic turbine generator can be applied.
As for power line supplied from two power supply sources of which both terminals are connected through other power lines, auto-recloser should be equipped to such power lines.
1. In case that two or three connecting power lines can be interrupted at the same time
- Asynchronous auto-recloser can be mainly applied to power linewith voltage from 110kV to 220kV if the above-mentioned conditions on application of asynchronous auto-recloser are satisfied.
- Synchronous auto-recloser can be applied if the above-mentioned conditions on application of asynchronous are not satisfied.
At important power lines of which the both terminals are connected through other power lines, if asynchronous auto-recloser cannot be applied to the two of them due to failure of theabove mentioned conditions on application of asynchronous auto-recloser, 1-phase auto-recloser, quick-act 3-phase auto-recloser or auto-recloser for auto-synchronization can be applied.In this case, 1-phase auto-recloser and 3-phase quick-act auto-recloser should be usedtogether with synchronous autorecloser.
2. In case that the both terminals of the power line are connected by the other no less than 4 power lines and two among the these connecting power lines is difficult to interrupt simultaneously, asynchronous auto-recloser should be applied.
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As for auto-recloser with synchronous check, first auto-reclose at one terminal of the power line should be carried out with voltage check and synchronous check. And second auto-reclose at the other terminal should be carried out with only synchronous check. In such way of auto-reclose, the order of the auto-reclose shall be changeable.
Several types of 3-phase auto-recloser at the same time on power line such as 3-phase quick-act autorecloser or 3-phase auto-recloser with synchronous check can be used. Different types of auto-recloser can be applied to each terminal of power line as follows.
-3-phase auto-recloser with voltage check is applied to one terminal.
-3-phase auto-recloser with voltage check and synchronous check is applied to the other terminal
In case that auto-reclose causes asynchronous energizing of synchronous compensators and that such energizing is unallowable for these synchronous compensators, in order to avoid supplying electric power from such synchronous compensators to fault point, the synchronous compensator should be disconnected from power system in case of power outage or should be made to operate without voltage by extinguishing its magnetic field. After voltage is recovered by successful operation of autorecloser, the synchronous compensator should be energized or synchronized again automatically.
For a transformer substation where synchronous compensator is installed,the measures to avoid wrong operation of automatic load shedder by frequency duringoperation of auto-recloser should be taken.
Article 505. Condition of Single Phase Auto-reclosers
One-phase auto-recloser shall be arranged so that it can be kept from operation in caseofloss of power supply, and it has to make automatically the protective relay on the power line operate to interrupt all phases of the power line without operating auto-recloser.
Fault phase in case of earth fault shall be indentified by selector. Such device can be used as auxiliary protective relay of one-phase auto-recloser in case that 3-phase auto-recloser, 3-phase quick-act autorecloser or operator energizes circuit breaker from either side of the power line.
The operating time of one-phase auto-recloser shall be calibrated according to the time sufficient to extinguish arc and for deionization at the field around 1 phase earth fault point in non-full phase mode, provided that the protective relays at the both terminals don’t operate for interruption.
1-phase auto-recloser can be combined with 3phase- auto-recloser. 3-phase auto-recloser should be prohibited to operate in case that 1phase- auto-reclose is not successful. In such case, -3phase autoreclose should be implemented at the either terminal of the power line with voltage check on the power line with time delay.
As for the decision of operating procedure of autorecloserwhich is composed of phase1autorecloser ant 3-phase auto-recloser, the operating procedure shall be considered based onhet actual operation method of the relevant power lines and in reference to Article 504.
Article 506. Required Functions to Prevent Malfunction of Circuit Breakers
When auto-recloser fails to operate properly, the other circuit breakers are prohibited to be closedIf. the other circuit breakers are closed in this case, the circuit breakerwhich failed to operate at autoreclose will be energized again, and accordingly, the range of the electrical failure will be extended. In order to avoid such extension of the electrica failure, the aforesaid operation of the circuit breaker is strictly prohibited.
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