Electrical Substation

1. INTRODUCTION Electrical substation for distribution system is the main supply to convert the high voltage (HV) to low voltage (LV) and the place where load are distributed to the consumers. In Malaysia, Tenaga Nasional Berhad Distribution (TNBD) used the 33/0. 433kV, 22/0. 433kV, 11/0. 433kV and 6. 6/0. 433kV voltage system for the electrical system to supply for domestic consumer and industrial consumer such as factory which will supplied directly from Transmission Main Intakes (PMU), Main Distribution Sub –station (PPU) or Main Switch Sub – station (SSU).

Electrical substation is the place where all electrical equipments such as high voltage switching, three phase transformer, high voltage cables, low voltage cables, low voltage feeder pillar, battery charging and etc which are used for electrical supplying in power system and to make sure the safety of the system by the protection scheme. Basically, electrical system have one or several in coming and out going circuit which are controlled by high voltage switching and meet in one or more in the same of busbar system.

Generally, electrical substation is a point in distribution system where: * A place where several electrical equipments are installed and used for electrical energy in power system. * A place where the safety of the system is provides by automatically protection scheme. * A place where one or several incoming and outgoing circuit are met at one or more busbar system and controlled by high voltage switching equipment which is used for switching. * A place where voltage value is changed and controlled. A place where load are distributed, controlled and protected FUNCTIONS OF A SUBSTATION * Supply of required electrical power. * Maximum possible coverage of the supply network. * Maximum security of supply. * Shortest possible fault-duration. * Optimum efficiency of plants and the network. 2. OPERATION OF 11 kV MODULAR POWER PLAN LAB 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.

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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. The stepped-down voltage of 11kV is channelled to the RMU(Ring Main Unit) and outgoing feeder of the substation.

This is to ensure the continous supply of electricity even during maintenance. The RMU unit is speacially designed that during maintence the affected users will receive supply from a different substation which is interconnected. This is because maintenance have to be carried out in an ON condition. 3. BLOCK DIAGRAM OF 11kV MODULAR POWER PLAN 4. FUNCTIONS AND MAINTAINENCE OF ALL EQUIPMENTS 5. 1 Switch gear/ circuit breaker In an electric power system, switchgear is the combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment.

Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is important because it is directly linked to the reliability of the electricity supply. Typically, the switchgear in substations is located on both the high voltage and the low voltage side of large power transformers. The switchgear on the low voltage side of the transformers may be located in a building, with medium-voltage circuit breakers for distribution circuits, along with metering, control, and protection equipment.

For industrial applications, a transformer and switchgear line-up may be combined in one housing, called a unitized substation or USS. Types of circuit breakers: I. Oil Oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc. II. Gas Gas (SF6) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the SF6 to quench the stretched arc. III. Vacuum Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched to a very small amount (<2–3 mm).

At or near current zero the arc is not hot enough to maintain a plasma, and current ceases; the gap can then withstand the rise of voltage. Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 35,000 volts. Unlike the other types, they are inherently unsuitable for interrupting DC faults. Maintenance 1) Visual Maintenance * To observe the switchgear to check any physical damage. 2) Insulation Test * Should be less then 40 ? with insulation resistance more than 100M?. 3) Change of oil. The oil in the switch gear tank need to be replaced in a period of time as it will become dirtier. 5. 2 Transformer A transformer is a power converter that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding.

This effect is called inductive coupling. Maintenance 1) Routine maintenance * Done once a week. Normal checkout throughout the transformer. 2) Preventive maintenance * For phase to phase or phase to neutral,nsulation test will be done by setting value of resistance more than 100M?. For LV to earth ,insulation must exceed 50M?. 3) Visual maintenance * To observe the transformer to check for any physical damage. 5. 3 Low voltage feeder pillar The low voltage feeder pillar comprises of the following components : * Feeder Pillar Enclosure Busbars * Current Transformer * Instrument Panel * Incoming Units * Outgoing Units Maintenence 1) Routine inspection. * Usually done to check for simple problem and fault. 2) Examination and service. * Do a full check up on all the instrument in feeder pillar such as the disconnectors ,enclosures whether it is in good conditon or need to replaced. 5. 4 Cable Used to convey electric current for the HV and LV system. At HV side, a 3 core cable is used while at LV side a 4 core cable is used. Maintainence 1) Visual inspection Observe the RMU to check for any physical damage. 2) Continuity test * To check if the current flow in the cable. 5. ELECTRICAL SAFETY RULES I. All elctrical equipment is to be assumed as in ON condition. II. All the maintenance work should be done inOFF circuit. III. Study FULLY about the instrument before operate or disturbed it. IV. Do not CLOSE any of the switch unless you are familiar with it and know how to control it whether in on or off condition. V. Do not TOUCH any electrical parts or body unleess you are not sure wheter the instrument is DEAD and EARTHED.

VI. Do not disconnect EARTHING connection or render ineffective the safety gadgets installed in the main apparatus. VII. Do not allow unauthorized person to handle HV electrical apparatus. 6. DISCUSSION Substations are part of the electricity supply network that enables the widespread use of electricity at home, work, places for education, leisure, commerce, health care, etc. The size of substations can be very variable, depending on whether they serve mainly residential properties, or also commercial and industrial units, etc.

Schools and institutions such as hospitals often have their own substation. There is a voltage clearance in substation where 15kV-138kV the clearance is 10 feet and 345kV is 18 feet. All maintainence workers must wear proper PPEs(Personal Protective Equipment) when entering the substation area. Substations are not hazardous because they are substations. It is because they are surrounded by electromagnetic fields that the equipment and cables they contain produce, that they have to be treated with caution.

Measured electromagnetic fields such as those produced by substations have been associated with health effects such as cancer, depression, dementia, infertility, miscarriage, heart problems, etc. There are two types of electromagnetic fields produced by overhead and underground cables and the substation equipment itself; electric fields and magnetic fields. The strength of the electric field depends on the voltage. Electric fields from substation equipment are unlikely to extend beyond the equipment housing, as they are screened by practically all building materials.

Magnetic fields are caused by electric current flowing when people use electrical power. For all practical purposes magnetic fields cannot be stopped and will travel through walls as if they were not there. There may also be underground cables leading to or away from the transformers. Electric and magnetic fields also come from underground cables. The electric fields will be zero as they are screened by earth, concrete, sand etc. The magnetic fields are very high near to the cable, higher than from overhead cables because they are closer to you.

They fall off more rapidly than the fields from overhead wires, because the cables are closer together and cancel out each other's effects more quickly. 7. CONCLUSION The overall operation system of a power substation is very important for electricity distribution. Where it is also important to supply power to users, it is also important to ensure safety is always prioritized. All the equipments must undergo regular maintenance to make sure they are working properly and prevent accidents. A log must be entered for each maintenance done so the history of the substation can be tracked. This to help future upgrades and for records.

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