Busbar system pdf

Some of the elements like bends, tees and other item which required welding are processed in MIG welding machine 2. Projection welding 3. Grinding and sandering section 4. Powder coating. Raw material for conductor is either 1. Aluminium- Copper- During training period I get a learning experience and acquired valuable knowledge about busbar trunking system. The company is engaged in engineering, manufacture and development of a wide variety of electrical equipment for power generation, transmission and utilization of electrical power and energy.

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Bijaya Kumar Mohanty. Natarajan Ramakrishnan. Adhish Gupta. Red Lopez. 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 Equation On the other hand, if RR is large IR is approach provides both the necessary information and the reduced.

The current transformers will have an excitation curve It is clear that, by increasing RR, the spill current IR can be which has not so far been related to the relay setting reduced below any specified relay setting. RR is frequently voltage, the latter being equal to the maximum nominal increased by the addition of a series-connected resistor voltage drop across the lead loop and the CT secondary which is known as the stabilising resistor. Under in-zone fault voltage drop in the relay circuit at setting current that is conditions it is necessary for the current transformers to important.

The relay can be designed as a voltage produce sufficient output to operate the relay. This will measuring device consuming negligible current; and be achieved provided the CT knee-point voltage exceeds provided its setting voltage exceeds the value Vf of the relay setting. In order to cater for errors, it is usual Equation In fact, the to specify that the current transformers should have a setting voltage need not exceed Vf, since the derivation knee-point e.

So a safety margin is built-in if the voltage setting is made equal to Vf. The limiting condition, will be of the same form. If the relay secondary effective setting is the sum of the relay requires more time to operate than the effective duration minimum operating current and the excitation losses in of the d.

This summation should this factor can be ignored and only the symmetrical strictly speaking be vectorial, but is usually done value of the fault current need be entered in Equation arithmetically. It can be expressed as: The In this case, the factor has become less than unity, secondary setting is converted to the primary operating possibly as low as 0. It is therefore possible to rewrite current by multiplying by the turns ratio of the current Equation Desirable as this In the case of a scheme exclusively for earth fault safeguard may be, it will be seen that it is better not to protection, the minimum earth fault current should be increase the effective current setting too much, as this considered, taking into account any earthing impedance will sacrifice some speed; the check feature in any case, that might be present as well.

Furthermore, in the event maintains stability. The primary operating current must which may lead to an excessive setting. In order to achieve phase and earth fault scheme, mainly to reduce the high-speed operation, it is desirable that settings should number of current transformers paralleled into one group.

The transient component of the Extra-high-voltage substations usually present no such fault current in conjunction with unfavourable residual problem. Using the voltage-calibrated relay, the current consumption can be very small.

For phase fault schemes, area and reduces the risk of accidental operation. It is possible that special circumstances section breakers.

The cable from the ring to the relay instability under any through fault condition. Supervision can be carried out to detect such conditions When the reserve bar is split by bus section isolators and by connecting a sensitive alarm relay across the bus the two portions are protected as separate zones, it is wires of each zone. For a phase and earth fault scheme, an internal three-phase rectifier can be used to effect a necessary to common the bus wires by means of auxiliary summation of the bus wire voltages on to a single alarm contacts, thereby making these two zones into one when element; see Figures The alarm relay is set so that operation does not occur with the protection system healthy under normal load.

Since a relay of this order of sensitivity is likely to It is shown in Equation This should therefore be Current transformers must have identical turns ratios, kept to a practical minimum. Taking into account the but a turns error of one in is recognised as a practical physical laying of auxiliary cables, the CT bus reasonable manufacturing tolerance.

Also, they should wires are best arranged in the form of a ring around the preferably be of similar design; where this is not possible switchgear site. The usual Current transformers for use with high impedance routing of cables on a double bus site is as follows: protection schemes should meet the requirements of a. With large current ratio.

The voltage can be limited advantageous to keep the secondary fault current low; without detriment to the scheme by connecting a this is done by making the CT turns ratio high. It is ceramic non-linear resistor in parallel with the relay common practice to use current transformers with a having a characteristic given by: secondary rating of 1A. C of for relay voltages up to V and one with a Under in-zone fault conditions, a high impedance relay Simple transformers, leading to the development of a high fast-operating relays would have a low safety factor voltage; the voltage waveform will be highly distorted constant in the stability equation, Equation The performance is improved saturation voltage.

Most modern busbar protection schemes use It must be recognised though that the use of any technique this technique. Current transformer secondary circuits are not switched directly by isolator contacts but instead by isolator repeat relays These switching relays form a replica of the busbar within the For an internal fault, and with no through fault current protection and provide the complete selection logic.

With low impedance biased differential schemes particularly where the busbar With some biased relays, the stability is not assured by installation has relatively few circuits, these magnetising the through current bias feature alone, but is enhanced currents may be negligible, depending on the value of IS.

The basic relay setting current was formerly defined as the minimum current required solely in the differential The through current will increase the effective relay circuit to cause operation — Figure From Equation This has been identified [ In this a Superseded definition b Current definition way the differential circuit of the relay is prevented from Figure So the greatest number of current transformers in parallel.

Position operating current that is just greater than the maximum transducers that follow the opening and closing of the load current, to prevent the busbar protection from isolators may provide the latter. This consideration multiple busbar systems where the isolators switch the is particularly important where the check feature is either auxiliary current transformer secondary circuits via not used or is fed from common main CT's.

These relays form a replica of the busbar and perform the necessary logic. It is therefore necessary to route all the current CT's is required. This seems to contradict the general Some installations have only one set of current principle of all busbar protection systems with a check transformers available per circuit. Where the facility of feature that complete duplication of all equipment is a check zone is still required, this can still be achieved required, but it is claimed that the spirit of the checking with the low impedance biased protection by connecting principle is met by making operation of the protection the auxiliary current transformers at the input of the dependent on two different criteria such as directional main and check zones in series, as shown in Figure This may be an attractive compromise when only one set of main CT's is available.

Check Check zone zone For optimum discrimination, the current The Type MBCZ scheme conforms in general to the In modern busbar protection schemes, the supervision of principles outlined earlier and comprises a system of the secondary circuits typically forms only a part of a standard modules that can be assembled to suit a comprehensive supervision facility.

Additional modules can be added at any time as the busbar is extended. A separate module is used for each circuit breaker and In addition to these It is a common modern requirement of low impedance there is a common alarm module and a number of power schemes that none of the main CT secondary circuits supply units. Ratio correction facilities are provided should be switched, in the previously conventional manner, within each differential module to accommodate a wide to match the switching of primary circuit isolators.

In practice the modules are mounted is to add a resistor to the differential path.