After the electrical discharge incident in November 2017 at Nguyen Hoang medium-voltage switching station, Mr. Truong Thai Son discovered the local discharge at the Hung Vuong - Nguyen Hoang 3 medium-voltage circuit breaker chamber. Both busbars C44 and C43 feature the very low insulation index. The busbar supports, terminal insulators of circuit breakers and medium-voltage circuit breaker are all wetted because the dryer resistors are damaged and cannot operate.
Mr. Truong Thai Son (right side) shares his experiences with young colleagues
After working with his colleagues to review and study the incident thoroughly, Mr. Son has proposed 03 solutions as follows:
1. Increasing the insulation level of the medium-voltage circuit breakers
In order to achieve the required operating values, the phase-to-casing and phase-to-phase insulation values of the medium-voltage circuit breaker must be not less than 1000 megaohms. When the busbar chambers get wetted, the insulation values of the circuit breakers are reduced, not meeting the required operation. Therefore, it is required to clean the chambers, use the gas burners to dry the chambers, and at the same time, impregnate varnish to seal the surfaces of the supports and brushes, and protect the equipment against moisture.
The devices in the busbar chambers, RMU circuit breakers, LBS, supports, medium-voltage TI and TU measuring and metering equipment are all made of refractory materials, so the method of heating by burners and varnish impregnation is widely used for quick repair to put the equipment back into operation as soon as possible, and reduce the time and effort.
2. Handling the refractory terminal insulators of medium-voltage circuit breakers
When the refractory terminal insulators of medium-voltage circuit breakers get seriously wetted, there are traces of discharge on the terminal insulators and terminals, it is required to dissemble the insulators, flush to clean with clean water, remove the traces of stain and discharge, then, dry them before heating by gas burners, re-measure the terminal insulation values of insulators and their pedestals to check whether they meet the requirements.
In addition, it is required to clean, heat and impregnate varnish at medium voltage for busbar supports and disc insulators for TU chamber in busbar chamber. The insulation values of busbars C43 and C44 must be higher than 1000 megaohms.
After the Electrical Test Center conducts the test and calibration of medium-voltage circuit breakers, the busbars C43 and C44 can be put into operation only when they are eligible.
3. Improving the dryer resistor boxes for the medium-voltage circuit breaker chambers at busbars
The resistance wires of the 200W/220V dryer resistor boxes are environmentally exposed, so they are susceptible to oxidation and have the short service life.
Solutions:
- The dryer resistors are embedded in glass tubes with the capacity of 200W/220V. The rectangular aluminum boxes are fabricated to form the heat extraction routes for supporting the dryer resistor tubes, and connected to the power supply through heat-resistant conduits and domino insulators.
- The dryers are improved to increase their service life and reduce the heat concentration at the resistors by using 02 series glass resistor tubes with the capacity of 400W/220V. At that time, the heat concentration reduces significantly, (not reddening anymore). Each resistor will work at 1/2 of voltage, so it will be more durable. In addition, the rectangular aluminum boxes are fabricated appropriately to form the heat extraction routes for supporting two resistor tubes and wiring safely through domino insulators and heat-resistant conduits.
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Mr. Truong Thai Son:
- Vice Leader of Grid Management Group 1 (Grid Management Team - Cho Lon Power Company);
- Being named as the "King of Initiatives" EVNHCMC;
- Setting up nearly 30 initiatives which have already been implemented, benefiting over VND 1.6 billion;
- Being granted the Merit Certificate of Creative Labour of the Viet Nam General Confederation of Labour, Class-III Labour Medal, Nguyen Duc Canh Award and many certificates of merit from the ministries, agencies and the People's Committee of Ho Chi Minh City.
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