Types of busbar pdf

The separate zones are arranged to overlap the busbar section switches, so that a fault on e. This Of these, a is suitable for small substations only, while has sometimes been avoided in the past by giving the d and e are obsolete.

Detailed discussion of types b Busbar P rotection section switch a time advantage; the section switch is and c occupies most of this chapter. Early forms of biased differential protection for busbars, such as versions of 'Translay' protection and also a Only the zone on the faulty side of the section switch scheme using harmonic restraint, were superseded by will remain operated and trip, the other zone resetting unbiased high impedance differential protection.

This gain, applicable only to very infrequent section switch faults, The relative simplicity of the latter, and more importantly is obtained at the expense of seriously delaying the bus the relative ease with which its performance can be protection for all other faults.

This practice is therefore calculated, have ensured its success up to the present not generally favoured. Some variations are dealt with day. There But more recently the advances in semiconductor are many combinations possible, but the essential technology, coupled with a more pressing need to be able principle is that no single accidental incident of a to accommodate CT's of unequal ratio, have led to the secondary nature shall be capable of causing an re-introduction of biased schemes, generally using static unnecessary trip of a bus section.

Such a failure, leaving aside the metalclad busbars e. SF6 insulated busbars. However, question of consequential damage, may result in disruption of the power system to an extent as great, or it has often been quite common for a unit protection greater, than would be caused by an unwanted trip.

The scheme to be used in addition, to provide two separate relative risk of failure of this kind may be slight, but it means of fault detection. Overcurrent protection will only be applied to H G J K relatively simple distribution systems, or as a back-up protection, set to give a considerable time delay. Distance protection will provide cover for busbar faults with its second and possibly subsequent zones.

In both Frame-earth fault relay Neutral cases the busbar protection obtained is slow and suitable check relay only for limiting the consequential damage. Here, the busbars are included, in sections, in the individual zones of the main circuit protection, whether this is of unit type or not. There are several standing it on concrete.

Care must be taken that the variations of frame leakage schemes available, providing foundation bolts do not touch the steel reinforcement; Busbar P rotection busbar protection schemes with different capabilities. A considerable number of schemes are still in service and The insulation to earth finally achieved will not be high, frame leakage may provide an acceptable solution in a value of 10 ohms being satisfactory.

However, the need to insulate When planning the earthing arrangements of a frame- the switchboard frame and provide cable gland leakage scheme, the use of one common electrode for insulation and the availability of alternative schemes both the switchgear frame and the power system neutral using numerical relays, has contributed to a decline in point is preferred, because the fault path would use of frame leakage systems.

In addition, if the involves simply measuring the fault current flowing from electrode earthing the switchgear frame is the offender, the switchgear frame to earth.

A current transformer is the potential of the frame may be raised to a dangerous mounted on the earthing conductor and is used to energize value. The use of a common earthing electrode of a simple instantaneous relay as shown in Figure When the system is resistance earthed, the allowed.

This requirement is so that: earthing connection from the switchgear frame is made between the bottom of the earthing resistor and the a.

An increased effective setting Figure If the earth scheme insulation resistance is too low, sufficient current may flow to operate the frame-leakage relay, and, as the check If it is inconvenient to insulate the section switch frame feature is unrestricted, this will also operate to complete on one side, this switch may be included in that zone. It the trip circuit. For this is illustrated in Figure Insulation All cable glands must be insulated, to prevent the barrier circulation of spurious current through the frame and earthing system by any voltages induced in the cable Zone G Zone H sheath.

Preferably, the gland insulation should be provided in two layers or stages, with an interposing K layer of metal, to facilitate the testing of the gland J L insulation.

A test level of 5kV from each side is suitable. When the busbar is divided into sections, these can be protected separately, provided the frame is also sub-divided, the sections mutually insulated, and each provided with a separate earth conductor, current transformer and relay. The individual zone relays Figure Faults in the low voltage auxiliary wiring latter case it is essential that this source of supply be must also be prevented from causing operation by connected to the side of the switchboard not containing passing current to earth through the switchgear frame.

Further, if possible, it is preferable A useful check is provided by a relay energised by the that an earthed source of supply be provided on both system neutral current, or residual current. If the neutral sides of the switchboard, in order to ensure that any check cannot be provided, the frame-earth relays should faults that may develop between the insulating barrier have a short time delay.

Of fault current and an operating time at five times setting the two arrangements, the first is the one normally of 15 milliseconds or less. It is not generally feasible to separately insulate the metal enclosures of the main and auxiliary busbars. Zone bus wires auxiliary switches The protection relays used for the discriminating and check functions are of the attracted armature type, with Figure The tripping circuits cannot be complete unless both the discriminating and check relays operate; this is because The tripping relays are of the should be provided to guard against such contingencies attracted armature type.

This will give earth a. This arrangement has b. To enable the protection equipment of each zone to be The phase and earth fault settings are identical, and this taken out of service independently during maintenance scheme is recommended for its ease of application and periods, isolating switches - one switch per zone - are good performance. The zones so formed are zone such as a busbar.

The principle is a direct over-lapped across the section switches, so that a fault application of Kirchhoff's first law. Usually, the on the latter will trip the two adjacent zones. This is circulating current arrangement is used, in which the illustrated in Figure A relay Tripping two zones for a section switch fault can be connected across the CT bus wires represents a fault avoided by using the time-delayed technique of Section path in the primary system in the analogue and hence is However instantaneous operation is the not energised until a fault occurs on the busbar; it then preferred choice.

The fault shown will cause operation of the busbar united through the circuit isolators during the transfer protection, tripping the circuit breaker, but the fault will operation. It is necessary for the bus protection to intertrip the far end of the circuit protection, if the latter Ideally, the separate discriminating zones should overlap With reference to Figure For this arrangement it is flowing.

Under these conditions, the protection can necessary to install current transformers on both sides of initiate an intertrip to the remote end of the circuit. This the circuit breakers, which is economically possible with technique may be used, particularly when the circuit many but not all types of switchgear.

With both the includes a generator. In this case the intertrip proves that circuit and the bus protection current transformers on the fault is in the switchgear connections and not in the the same side of the circuit breakers, the zones may be generator; the latter is therefore tripped electrically but not overlapped at the current transformers, but a fault shut down on the mechanical side so as to be immediately between the CT location and the circuit breaker will not ready for further service if the fault can be cleared.

This matter is important in all switchgear to which these conditions apply, and is The conditions are location. A single mesh corner is shown in Figure Busbar P rotection shown in Figure Current transformers mounted on both sides of breaker protection -no unprotected region b.

Current transformers mounted on circuit side only of breaker Note 2: Multiple circuits may be connected -fault shown not cleared by circuit protection to the mesh corner b CT arrangements for protection - additional mesh corner protection required Figure Where only one connection to the mesh is An equivalent circuit, as in Figure However, this arrangement cannot be used where more than one connection is made to a mesh corner.

This is because a fault on any of the connected circuits would result in disconnection of them all, without any means of determining the faulted connection. The considerations that have to be taken into account are detailed in the following sections. These circuits can then be the current transformers is not detrimental as long as it Busbar P rotection interconnected as shown, with a relay connected to the remains within the substantially linear range of the junction points to form the complete equivalent circuit.

With fault current of appreciable magnitude and long transient time constant, Saturation has the effect of lowering the exciting the flux density will pass into the saturated region of the impedance, and is assumed to take place severely in characteristic; this will not in itself produce a spill current transformer H until, at the limit, the shunt output from a pair of balancing current transformers impedance becomes zero and the CT can produce no provided that these are identical and equally burdened.

This condition is represented by a short circuit, A group of current transformers, though they may be of shown in broken line, across the exciting impedance. It the same design, will not be completely identical, but a should be noted that this is not the equivalent of a more important factor is inequality of burden. In the physical short circuit, since it is behind the winding case of a differential system for a busbar, an external resistance.

Severe unbalance is In the event of a fault, the circuit breaker breaks, and the defective section of the busbar is easily disconnected from the circuit. Busbars are mainly available in rectangular, cross-sectional, round, and many other shapes. Rectangular bus strips are mostly used in power systems.

Copper and aluminum are used for the production of electrical bus bars. A variety of busbar configurations are used in the electrical power system. The choice of a busbar depends on various factors such as reliability, flexibility, cost, etc. In small substations where there is no constant need for power, a single busbar system is used. But more than one busbar is used in a large substation as compared to a smaller substation.

Due to which the problem of power trips does not arise. The design of the Single Bus-Bar Arrangement is simple and easy. Only one busbar is connected to the switch system. All substation equipment like a transformer, generator, feeder are connected only to this bus bar. This type of busbar system uses an isolator and a circuit breaker as a switch.

The defective part is separated with the help of an isolator. So that the entire power system is protected by a complete shutdown. This system uses more than one circuit breaker which makes a slight difference in the cost of the system. In such a system two busbars are used, the main busbar and transfer busbar The busbar system uses a bus coupler that connects the different switches that connect the circuit breaker to the busbar.

A bus coupler is used to shift the load from one bus bar to another busbar crossing in case of power overload. In large generating stations, where several units are installed, it is a common practice to sectionalize the bus as illustrated in Fig. Normally the number of sections of a bus-bar are 2 to 3 in a substation, but actually it is limited by the short-circuit current to be handled. In a sectionalized bus-bar arrangement only one additional circuit breaker is required which does not cost much in comparison to the total cost of the bus-bar system.

Such an arrangement provides three main advantages over simple single bus-bar arrangement:. Firstly, in the event of occurrence of fault on any section of the bus-bar, the faulty section can be isolated without affecting the supply of other section or sections. Secondly, one section can be completely shut-down for maintenance and repairs without affecting the supply of the other section s. Thirdly, by adding a current limiting reactor between the sections the fault level MVA can be reduced thereby circuit breakers of lower capacity can be used.

At times air-break isolators were used in place of circuit breakers as bus-sectionalizer due to economy, but it must be remembered that any isolation affected by them must be affected under off-load conditions otherwise it may cause spark. It will be preferable to provide circuit breaker as a sectionalizing switch so that uncoupling of bus-bar may be carried out safely during load transfer. A double isolation is however necessary when the circuit breaker is employed as sectionalizing switch so that the maintenance work can be carried out on circuit breaker while the bus-bars are alive.

This arrangement has been quite frequently adopted where the loads and continuity of supply justify additional costs. This arrangement provides additional flexibility, continuity of supply and allows periodic maintenance without total shutdown.

Such an arrangement is suitable for highly interconnected power network in which flexibility is very important. Figure Such an arrangement consists of two bus-bars, known as main bus-bar and transfer bus-bar used as an auxiliary bus-bar. It ensures continuity of supply in case of bus fault.

In the event of occurrence of fault on one of the bus, the entire load can be transferred to the other bus. Repair and maintenance can be carried out on the main bus without interrupting the supply as the entire load can be transferred to the auxiliary bus.

The in-feed and load circuit may be divided into two separate groups if required from operational considerations. The testing and maintenance of feeder circuit breakers can be done by putting them on spare bus, thus keeping the main bus undisturbed. The bus is maintained or expanded by transferring all of the circuits to the auxiliary bus depending upon the remote backup relays and breakers for removing faults of the circuits.

During this condition a line fault on any of the circuits of the bus would shut-down the entire station. In very important power stations two circuit breakers are employed for each circuit, as illustrated in Fig.

Such a bus-bar arrangement does not require any bus-coupler and permits switch-over from one bus to the other whenever desired, without interruption. This bus arrangement is very costly and its maintenance cost is also high. This arrangement provides maximum flexibility and reliability as the faults and maintenance interrupt the supply to the minimum. A circuit breaker can be opened for repairs and usual checks and the load can be shifted on the other circuit breaker easily.

But because of its higher cost, this arrangement is seldom used at the substations. For kV switchyards two main buses plus one transfer bus scheme is preferred. The transfer bus is used for transferring power from main bus 1 to main bus 2 and vice versa.

In this arrangement duplicate bus-bars are used with the main bus-bar in sections connected through a bus-coupler, as illustrated in Fig. In this arrangement, any section of bus-bar can be isolated for maintenance, while any section may be synchronised with any other through the auxiliary bus-bar.

Sectionalization of auxiliary bus-bar is not required and would increase the cost if done. This is an improvement over double bus double breaker arrangement and it affects saving in the number of circuit breakers.