129740-002 ABB card PLC module DCS system spare parts servo controller

Description

129740-002 ABB card PLC module DCS system spare parts servo controller

When the gas relay uses the internal fault of the transformer to make the oil tap produce gas or cause the oil flow surge, the gas relay contacts will act to send out alarm signals (light gas) or automatically cut off the transformer (heavy gas). Light gas mainly reflects operation or minor fault (such as overload heating, local heating of iron core, heating of oil tank due to magnetic leakage, etc.), when the gas decomposed by oil rises and enters the gas collecting chamber of gas relay, the 129740-002 air pressure makes the oil level slowly drop, the relay drops with the oil level, the light gas dry spring contact is connected to send a signal, and further drop of the oil level will cause heavy gas action. Heavy gas mainly reflects that when serious faults such as bushing grounding and interturn short circuit occur in the transformer, a large amount of gas is generated rapidly to push the oil flow to impact the baffle, and the magnet on the baffle attracts the heavy gas dry spring contact to conduct and trip.

2、 Cause Analysis of Light Gas Alarm
At present, there is only one gas relay for the main transformer and the voltage regulating transformer of the UHV AC transformer. The casing riser is connected to the gas relay of the main transformer through the gas collector. The gas relay of the UHV transformer has only one pair of light gas alarm contacts. In the normal operation state, the light gas is put into the alarm state and the heavy gas is put into the trip state.
The converter transformer is generally equipped with one gas relay (Siemens technical route) or seven or more gas relays (ABB technical route). In normal operation state, light gas is put into alarm state and heavy gas is put into tripping state.
The converter gas relay has only one or two pairs of light gas alarm contacts, which is easy to cause light gas signal action due to water ingress into the relay junction box, oil chromatography carrier gas entering the oil tank, poor sealing of the body and other reasons, and it is unable to take two out of three anti maloperation measures. If the light gas signal is tripped, the misoperation of the light gas signal will cause the DC monopole (single valve group) to trip, and the loss of 1500MW or more power may affect the stable operation of the power grid system. In addition, in case of minor faults such as transformer core and insulation slight heating and gas production, light gas acts correctly but heavy gas has not yet acted. After 129740-002 light gas alarm, there is a certain time for judgment and treatment on site, which can improve the availability of equipment. Therefore, 18 Major Anti accident Measures for Power Grid and Power Transformer Operation Regulations (DL/T572-2010) stipulate that light gas only alarms.
Misoperation case: In 2003, a converter station suffered a total loss of 1281MW due to the bipolar locking caused by water entering the junction box of the converter transformer flat anti gas relay; In 2019, a station was temporarily shut down due to the fault of the contact circuit of the converter gas relay.

3、 Suggestions on switching light gas into tripping mode for transformer
Considering the risk of sudden failure of UHV transformer equipment, which poses a serious threat to the personal safety of operators, it is recommended to change the alarm to trip after the light gas action of UHV transformer. The reason is:
First, light gas may act before heavy gas in case of sudden serious fault of transformer. In this case, if the light gas is tripped, the fault converter can be tripped in time to avoid major equipment accidents or casualties. In 2016, a certain transformer set fire after several times of high anti light gas alarms. On August 29, 2017, when the casing at the converter network side of a converter station failed, the light gas acted 32 seconds before the heavy gas.
Second, the grid structure of the current power grid system is continuously strengthened, and the loss of transmission power of a valve group or a group of transformers will no longer cause security and stability problems of the power grid.
Third, as the operation and maintenance unit vigorously strengthened the management of the converter non electric relay, carried out the installation of relay rain cover, regular relay spot check, regular inspection of circuit insulation and other work, which greatly reduced the risk of gas relay misoperation. The Equipment Department organized statistics on the light gas action of the converter station in the past three years and the substation in the past five years. The light gas did not misoperate, but only operated six times, of which four times were caused by the gas not discharged completely in the process treatment stage, It is not a device problem.
During the unstable state of the UHV transformer, it can be considered to raise the bushing at the converter network side to light gas, the bushing at the valve side to light gas, the tap changer to light gas, the body to light gas, and the main transformer and voltage regulating transformer to light gas for temporary tripping to ensure the safety of personnel and equipment.

4、 Implementation Scheme of Changing Light Gas Relay into Trip
In order to avoid the impact of power failure on the system mode arrangement, the converter can exit the modification software through the DC control single system, and change the UHV converter light gas action signal to trip. Since the signal circuit of the gas relay is checked every year, and the signal circuit is reliable, it is unnecessary to arrange a trip test after the modification of the program. In the future, it can be implemented in combination with the power outage opportunity, and the estimated duration is one day. The AC transformer can be changed from light gas to tripping by modifying the wiring of the protection screen, and the transmission can be carried out. The estimated construction period is one day.

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