Maintenance

i. Maintenance

19-30 of April (2 weeks)

Distribution

Basically 11 kV network is the main distribution voltage used by TNB. The 11 kv is stepped down from the 33 kv transmition voltage via power transformer in main intake distribution substation (PMU-Pencawang Masuk Utama) from the PMU the 11 KV is distributed into many feeders via main switch station (ssu) and each feeder consist of a few substance (PE) of 11 KV that stepped down to 415 V via step down power transformer. Sometimes PE called RMU switch gear.

There are various types of customers using the electricity with different voltage and phases :

Ø they use single

phase 240V for the normal houses.

Ø 3 phase 415V. For the consumption of high load in a three phase load such as a commercial category,

Ø For the industrial category there are 2 types :

I. LPC (large power consumer) which are 3 phase

2. 11KV directly from transmission line,

- 3 phase 33KV

Main intake substation PMU and main switch station SSU

The main intake substation (PMU) is a node for terminating and reconfiguring transformer that step down 33KV voltage to 11KV voltage (primary distribution level ) while the main Switch Station (SSU) is a node of terminating and reconfiguring the 11KV line of many feeders consisting of substation.

For the PMU and SSU sides,

the protection implantations at these sides are vacuum circuit breakers (VCB) .they are operated atomically when the current transformer sense the over current or the earth fault or maybe both of them ,and make the relay operate, while the mechanical part operates and motorizes the breaker option.

Substation PE

The electrical connection of the substation in putrajaya operated by TNB is in form of rings called Ring Main Unit (RMU), the connection is illustrated at the Sketching page.

The RMU switch gear is a ring main unit (rmu) connection of a switch that separates the feeder from the secondary distribution transformer.

Ø The substation consists of two main parts which are :

1. switch gear

2. transformer .

v Steps of how is the maintenance are for one of the substation in putrajaya, down is showing which substation they choose to maintain it.

o Substation no 17.05 feeder no 1 :

· Two teams are doing the maintenance

· The first team is to cutoff the supply from the substation 17.05 :

· Firstly they move to off point at ss2..01

· ON the switch feeder from OFF and keep the earth’s switch off.

· Moving to substation (PE17.04) to OFF the feeder from ON and remain the earth Switch OFF.

· Moving to substation (PE2.03) to OFF the feeder switch and remain the earth switch OFF.

· After making sure that all the feeder switch is OFF on the substation (to prevent any short circuit or fault) they turn ON the entire earth switch.

· Then at the substation (PE17.05) which want to service it first thing to make sure before starting the maintenance is to check the voltage indicator to know eitherthe voltage is still passingor dead

· If the light is on its mean there is still voltage atthe cable

· If the light is off it means the cable is dead.

· After cut off the supply the second team is starting the service after getting a safety rules from the person in charge.

Transformer service

During my visit to PPU located at precint 10, I have given a chance to see how MTM staff serviced the power transformer. On this day I went up onto the 11kv transformer and learned afew parts of the transformer such as:

Gas preservation system

Gas detector relay

Dehydration breathers

Oil to oil bushings

Power transformer that TNB usually use are on OTP (oil transformer planet) type. It is generally mixed with the Gas, water and contaminants. The content of the contaminants generally increase with time. In the oil treatment plants (OTP) these associated gases, water and contaminants are separated from the oil and taken away .in fact, it is electrically critical that the oil doesn’t contain too much of these substances. after treating the oil in the oil treatment plant, the stabilized oil is then again ready to be used in power transformer.

Tests

High voltage DC test.

Ø The tests are on switchgear to test the reliability of vacuum tubes on VCBs.

Ø Results :

1. Earth phase should be 240V.

2. Phase to phase voltage should be 415V.

3. The phase rotation must be red to red, yellow to yellow and blue to blue.

Insulation Resistance Tester.

Ø Tested to the cables and switchgear to check for possible leakage resistance failure.

Maintenance cycle

According to the maintenance policy, all the services for substation and main intake substation must be done according to the time cycle as well as the equipments brand. For example the 11 kV VCB (vacuum circuit breaker) of SIMEMENS or ABB must be serviced for every 18 months while VCB 33kv is 12 months from the time reviewed