SUBSTATION

Introduction

Electric power is normally generated at 11-25kV in a power station. To transmit over long distances, it is then stepped-up to 400kV, 220kV or 132kV as necessary. Power is carried through a transmission network of high voltage lines. Usually, these lines run into hundreds of kilometres and deliver the power into a common power pool called the grid. The grid is connected to load centres (cities) through a sub-transmission network of normally 33kV (or sometimes 66kV) lines. These lines terminate into a 33kV (or 66kV) substation, where the voltage is stepped-down to 11kV for power distribution to load points through a distribution network of lines at 11kV and lower.

1.      Transmission main intake ( pencawang masuk utama-PMU )

Transmission Main Intake is the interconnection point of 132kV or 275kV to the distribution network. The standard transmission capacity and voltage transformation provided at the PMU are as follows:-

- 132/33kV, 2 x 90 MVA
- 132 /22kV, 2 x 60 MVA
- 132 /11 kV, 2 x 30 MVA

2.      Main Distribution Substation (pencawang pembahagian utama-PPU )

Main Distribution Sub-station is normally applicable to 33kV for interconnecting 33kV networks with 11 kV networks. It provides capacity injection into 11 kV network through a standardized transformation of 33/11 kV.

3.      Main Switching Station ( stesen suis utama-SSU )

SSU at 33kV, 22kV and 11 kV are established to serve the following function:-

1. To supply a dedicated bulk consumer ( 33kV, 22kV, 11 kV)
2. To provide bulk capacity injection or transfer from a PMU/PPU to a load center for further localized distribution.

4.      Distribution Substation ( pencawang elektrik-PE )

Distribution sub-stations are capacity injection points from 11 kV, 22kV and sometimes 33kV systems to the low voltage network (415V, 240V). Typical capacity ratings are 1000kVA, 750kVA, 500kVA and 300kVA.

Conventional substation designs are of indoor type (equipment housed in a permanent building) and out-door type (ground-mounted or pole-mounted). Standardized M & E design of 11/. 433kV sub-station is available at TNB offices. Compact substation (11 /. 415kV) has limited application and is to be strictly applied in selective situations under the following circumstances:-

  § System reinforcement projects for highly built-up areas where substation land is difficult to acquire.

  § Any request to use compact substation for dedicated supply to a single or limited group of low voltage consumers is subject to TNB approval in accordance to site constraints situation, and to be considered as ‘special feature design schemes’.

SUBSTATION 

In the electrical distribution network, a sub-station has many components such as circuit breaker, transformer, and switches, fuses which must be housed properly to ensure continuous and reliable service. According to construction of sub-station, several factors need to be taken for the construction such as location and load demand

There have 4 types of sub-stations in electrical distributions network

1.      Indoor substation

2.      Outdoor substation

3.      Pole-mounted substation (H-pole)

4.      Compact substation

Components in substation

1.      Switchgears – not available in H-pole.

2.      Ring Main Unit – located in PPU only.

3.      Transformers

Protections

·         Protection Relays and Vacuum Circuit breaker (VCB) – located in PPU only.

·         Transformer Fuses

·         Isolating Switch – Located in H-Pole only

·         Pin Insulator – Located in H-Pole only

·         Low Voltage Fuses – Located in H-Pole only

·         Lightning Arresters – Located in H-Pole only

·         Earthling

Underground Cables

·         PILC

·         XLPE

Distribution Boards

·         Low Voltage Distribution board (LVDB)

·         Feeder Pillar

Substation work

I. Visual Inspection

Done once per 3 months

Done by seeing, hearing, smelling and feeling the substation and its equipment to see if there is anything wrong with the particular substation

If there were any defect, report to Authorized Person (AP) for corrective maintenance.

II. Routine Maintenance

Done once every 6 months

Take substation data, load reading

Work including cleaning and repairing inside and outside substation such as cut grass, throw rubbish repairing broken gate and take LV current Data reading at LVDB.

III. Preventive Maintenance

Done once every 18 months

Full maintenance from top to bottom, involving all of the equipment inside and outside the substation

Done by either the Substation Team or an outside contractor

Among the list of things to do include servicing the LV distribution board (LVDB), servicing the switchgears and servicing the transformers

Preventive Procedure

1. The monthly shutdown schedule was prepared and submit to RCC ( regional control center ) two month before.

2. Submit the actual shutdown schedule to RCC a month before.

3. After getting an approval from RCC, they will key in the data in online shutdown management system to print out the notices for consumer.

4. Sent the notice to consumer to let them know there will be no electricity supply during this time.

5.The authorized person (AP) will request a permission from controller for the shutdown process.

6.RCC will issue authorization to AP.

7. For safety , AP will issue a SKMK ( Sijil Kebenaran Melakukan Kerja ) or PTW ( Permit To Work ) to CP.

8. Started the preventive works.

9. CP ( competence person) will canceled the PTW and submitted to AP.

10. AP will canceled the Autorization that given by RCC.

11.Start switching again

12. After everything was back to normal ( electric supply was back again ) informed RCC.