Saturday, 19 July 2008

Testing & Commisioning 11-kV Sub-station

Typical 11/0.433-kV sub-station building (attached)

11-kV sub-station building normally houses 11-kV switchgear (Circuit Breaker, High Fuse Unit (HFU) or Load Break Switch (LBS), 11/0.433-kV Distribution Transformer and 415-V Low Voltage Switchboard. This three-room building normally measures 35' x 15' (10.6m x 4.6m) by TNB Standard or 39' x 15' (11.9m x 4.6m) according to JKR Standard.

As this building is the source of electricity supply to a new project, there is always an urgency that all the equipment be installed and commissioned before the other Mechanical and Electrical (M & E) equipment in the building are tested and put into service.

Thus, it is very important in all projects which receive the 11-kV supply (whether from TNB or exisiting 11-kV Main Intake Sub-station (MISS) or Main Switching Swithing (MSS) or Stesen Suis Utama (SSU - in Bahasa Malaysia) to properly test and commission every equipment installed inside the 11/0.433-kV sub-station before energizing or switching on the 11-kV supply to the said sub-station. This is imperative to ensure that the 400-V stepped-down 3-phase Low Voltage (LV) supply to be used for the Testing and Commissioning (T&C) of M&E equipment in the project does not experience any disturbance or causing any danger or untoward accident to the contracting personnel.

According to the Malaysia Electricity Regulations 1994, before any electricity supply to be given to a new premises, Forms G and H must be submitted to the Supply Authority for record and approval.
Form G denotes that a Competent Person has duly verified that he or she has carried out the supervision of the installation works (and it has been done according to the safety rules and regulations) while Form H submitted by the Competent Person who had confirmed that all tests have been carried out on all equipment which are to be energised and he has confirmed that it is safe to switch on the electricity supply to the 11-kV switchgear, transformer and LV Board.

Some of the basic tests on the equipment housed in the 11-kV sub-station are :

A. 11-kV Switchgear (Circuit Breaker or RMU)
1. Insulation Test 1 : using 5-kV DC
2. AC Pressure Test for 1 minute (record leakage current)
3. Insulation Test 2 : using 5-kV DC
4. Vacuum Check (if Vacuum Circuit Breaker is used)
5. SF6 gas check (if SF6 CB is used)
6. Calibration of all out-going circuits protection relays
7. Calibration of protection relays according to settings approved by TNB or Consultant
8. Insulation, Ratio (and pressure test) on 11/0.110-kV Potential Transformer
9. Insulation Test on incoming 11-kV cable (5-kV DC)
10. Pressure Test on 11-kV XLPE Cable (Very Low Frequency (VLF) = 19-kV AC for
60 minutes/phase)
11. Tripping Test on Transformer Alarm and Trip Temperatures
12. Verify and Test Earth Resistance

11-kV SF6 Ring Main Unit, Vermin-proof netting,
Grounding Copper Tape & Ventilation Louvred Opening

B. Distribution Transformer
1. Insulation Test (P-E, P-S, S-E)
2. Ratio Test (at every tap, 1 to 5)
3. Insulation Test on Primary and Secondary Cables
4. Verify Star-pint Neutral earth point and pit

11/0.433-kV 1000KVA ONAN Transformer : Alarm
& Trip connection; trenching, cable support

C. Main Switch Board (MSB or LV Board)
1. Calibrate all protection relays
2. Insulation Test on all out-going cables
3. Insulation Test on the main busbar
4. Check Earth Resistance
5. Ensure Voltage Surge Supressor (VSS) is earthed accordingly.

1600A 415-V Main Switch Board : relay
calibration, as-built drwgs, label, panel opening

Once all the test results are produced and verified by the Consulting Engineer/Designer and all tests have been verified by the Service Engineer, then only the 11-kV electricity supply be switched on the incoming Circuit Breaker/LBS.

There are other basic and important requirement such as Danger and No-Entry signages, 11-Kv and 415-V Switch Boards labelling, Rubber Mat, CPR Intruction Manual, As-built Diagram, etc. must be installed before or once the switchboards are energised.

Photographs below show some of the defects or non-compliances to Electricity Regulations of an 11-kV installation which has been energised !!!
It is hope that immediate actions are taken by the Project manager to ensure that the 11-kV installation does not cause any danger to the operating personnel within the vicinity of the 11-kV sub-station.

Some of the defects observed at the energised 11-kV sub-station are :

A. 11-kV Switchgear (Circuit Breaker or RMU)
1. There is no label at Ring Main Unit - Danger sign, etc.
2. Incoming and outgoing 11-kV cables are not properly or firmly supported;
3. 11-kV trench is still littered with waste materials (paper, wood, plastic, etc.)
4. No as-built drawing framed at the wall of the room;
5. LV Board shares the same room with the HT equipmnt (problem of competency personnel)
6. Louvred windows to be fitted with SWG23 Mesh 10 vermin-proff wire netting
7. Earth pit for 11-kV RMU earthing is not found/could not be located (identified)
8. 11-kV Log Book is to be provided
9. Temperature Alarm & Trip facilities at the RMU - could not be verified
10. Trench cover must be provided and the trench shall be filled with clean river sand
11. To test and verify Earth Resistance connected to HT panel

B. Distribution Transformer
1. 11-kV Primary cable termination is a bit doubtful (saddled with wood)
2. Cable trenches are not properly constructed and covered
3. Secondary cables (415V) are not properly saddled/bracketed to the side walls of trench;
instead the cables are 'pulling-down' the bus-bar attached to cable termination flags
4. PVC/PVC green cable used as star-point neutral is not properly terminated/linked/welded
to the earth electrode at the earth pit;
5. To verify whether the Alarm and TRip contacts are linked to the Ring Main Unit (RMU)

C. Main Switch Board (MSB or LV Board)
1. All protection relays were not calibrated by Service Engineer
2. Some of front metal panels could not be closed due to misalignment;
3. MCCB panels must be correctly labelled;
3. Short-circuit Current Rating (Isc) of some MCCBs are not 43-kA minimum
4. Power Factor correction capacitor bank is to be tested and commissioned
5. Cable trenches c/w cover is not properly installed (debris still littered at the bottom of the
6. Log book is to be provided;
7. CPR instruction framed-poster is to be installed inside the LV Room.

11/0.433-kV Tx : grounding pit, cleaniness,
cable trench, trench cover

Note : It is not the intention of the Inspector to find fault on the project execution. As a Service Electrical Engineer, I would like to say that legally and for safety sake, the sub-station and its related components SHOULD NOT BE ENERGISED YET as there are still impending job such as relay calibration, labelling, trench works, etc which were not done yet but are VERY IMPORTANT to ensure safety to the equipment and personnel handling it.