What is Busbar Protection : Types & Its Testing

Before knowing the concept of busbar protection, let us first know what a busbar is. So, a busbar is the electric one which is stated as either a single or array of conducted employed for accumulating electric power from the incoming feeder devices and delivers it to the outgoing feeder devices. It can also be defined as the junction where the intersection of incoming and outgoing feeders collide.

Therefore, an electric bus bar gathers power from a single location. The device is included with a circuit breaker and an isolator. At the time of faulty conditions, the circuit breaker gets tripped off and the damaged part gets detached from the circuit. Now, we shall move into the concept of busbar protection and various schemes of protecting?

What is Busbar Protection?

In the past, busbar protection is done through current relays and it is anticipated that any kind of transformer or feeder which is in connection with the busbar should not interrupt other busbar systems. Corresponding to this, the length of the current relays was increased. So, when damage takes place in the busbar, more time is required to disconnect the bus and this might cause more damage too.

While in recent days, the second zone length of the protection relays in regard to feeder devices having the functional time of 0.3 – 0.5 seconds was made in use for protecting busbars. But this scenario will not differentiate the damaged part of the busbar.

Currently, most of the power systems are dealing with a high range of power levels and disruption in the busbar will impose huge losses. So, it is more crucial to protect busbar systems. In view of this differential, busbar systems are used where these methods have functional time < 0.1 sec. The main importance of the busbar system is to enhance the dependability of the power system by sustaining the removal of power when there happens to trip in the feeder devices.

To know in detail, let us consider the below example. In the circuit which shows a faulty condition. In order to safeguard the device, it is needed to disconnect the faulty section from all the electric power resources as quickly as possible. This corresponds that circuit breaker sections 1, 2 3, and 4 should be in open condition while functioning of the busbar safety.

One may possibly be in the thought that only CB-1 should be open, but not. As all the feeder devices 2, 3, and 4 have connections with the grid, those might impose damage as the grid is the main power resource. On the whole, the entire feeders should be opened. The main operation of busbar protection is to detach the busbar system in faulty conditions.

Busbar Protection Schemes

There are various schemes used for busbar protection. The main schemes are detailly explained in this article today.

System Protection used to Cover Busbars

The system which is implemented to shield busbar protection is included with either overcurrent or distance safeguarding. With the implementation of this, busbars are essentially safeguarded. This method is even applied as a backup safeguard by the application of time grading at the condition when minimal protection activity is necessary.

The scenario of time grading makes sure that the circuit breaker which is close to the damaged section will be opened initially by selecting a suitable time setting for every relay. This scheme can be clearly understood by considering the below example.

Frame-Earth Protection

In the ancient days, these are mainly used as protection schemes. This approach can be implemented for multiple arrangements of busbars every arrangement has its own ability. This approach is still in implementation and they offer good efficiency too. The addition of numerical relays has decreased the usage of frame leakage methods.

There are other three types in the frame-earth protection schemes which are of:

Single Busbar Frame-Earth Protection

This scheme is used when there is an earth faulty system and is employed for the calculation of currents that flow from the switchgear to the earth frame. This method is designed in the way that the instant relay as displayed in the picture is stimulated by the current detected by CT which is placed on the earthing conductor. Here, it is important the switchgear has to be shielded from the ground by using concrete as a base.

Sectioned Busbar Protection

Here, the entire busbar system is partitioned into two sections and the protection also happens to each section. This can be achieved by separating each form into sections and each section is provided with an earth conductor. And also, every section has its own protecting relay and a CT.

These sections are now considered individual sections as depicted in the below picture. The design of this scheme is done in the way that the protective relay is tripped when the damage has happened internal to the corresponding section and the other section is not disturbed.

Double Bus Substation

Here, busbar protection is done for the entire bus added with more trip systems connected to the primary bus as shown in the below figure. A safety system is utilized in order to offer protection to the components from the actions that happened from functionality because of either mechanical or human shocks. This safety system is not suitable for minimal component systems.

When the damage is for minimal voltage wiring, then the safety system needs to obstruct the functionality happened because of current flow to the earth through the switchgear frame. The functionality is provided by stimulating the relay by using the neutral current.

When the safety system for the neutral current is not provided, then the frame earth relays will be activated after some time gap. These are the types of frame-earth busbar protection schemes.

Differential Protection for Busbars

This scheme directly implements the KCL principle where it is needed where the incoming currents are equivalent to the outgoing currents from a similar node. The system is considered as a fault when the sum of the currents is not equal to ‘0’ in correspondence to the phase or magnitude of the difference.

In this differential protection scheme, there are again other approaches of implementing these techniques and those are:

High Impedance

This scheme was in implementation for the past 5 decades due to its high robustness, quickness, and protected functionality. Here, the system utilizes voltage all through the differential junction nodes.

But the drawback of this type is that it needs concentrating CTs and it is highly economical. During the busbar damage, it also needs an extra voltage regulating resistor for energy absorption.

Low Impedance

This approach does not need any CTs. It holds the ability to withstand considerable CT overload at the time of external damages. This scheme even offers a correspondingly high range of tripping speeds. Using microprocessor-dependent relays in this system will augment the utilization because of its high-end algorithms for differential safeguarding operations.

Sectionalized Busbars

When the sectionalized busbars are implemented with a differential protection scheme it is needed that separated bus uses individual circulation currents. Here, zones are implemented to separate the sections and are constructed in the scenario that those will be intersecting all through the section switches so that the entire system is safeguarded.

In the case of a double bus bar arrangement system, two busbars are managed as individual sections. When the coupling takes place, these sections will get overlapped. Here, an isolator switch will be in connection with both the busbars. This has to be related to the suitable section through early make or late break supporting contacts. This makes sure that when the isolators are getting closed, then the supporting switches function before the primary contacts are operated.

Whereas when the isolators are in open condition, their primary contacts get opened in before the supporting switches. The secondary circuits of the two sections are temporarily paralleled and are connected across the circuit isolators at the time of transfer functionality.

Location of the Current Transformers

In the case of an ideal safeguarding system, the sections should be overlapped and they should have individual differential safeguarding systems, The circuit is designed in the way that the locations where the sections get overlapped, then there has to be a circuit breaker that covers both the sections. There has to be the installation of CTs on both the edges of the CB. This is the arrangement as it shields the entire main circuit.

The below picture shows that CTs are installed are located at one edge of the CB. This seems to be not ideal as it does not protect some portion of the main circuit. And this section is termed a short zone.

Reverse Blocking/Interlocking Protection

In the conventional type of protection systems, when damage takes place, it will be removed by using time delay upstream relays. Using a numerical method, this busbar locking approach can be implemented for safeguarding the distribution system using a single source. Here, time grading is necessary so as to synchronize the overcurrent relays to prevent faulty conditions. The main benefits of using this approach are:

• These schemes can be easily suitable for substation extensions
• This method needs minimal pricing when compared with the differential safeguarding method
• This approach has a quick damage resolution technique than that of the systems that use trip created by upstream feeder safeguarding. These are also termed zone sequence interlocking schemes.

These are the main busbar protection schemes.

Testing

To test a busbar protecting differential relay, it is needed to use a current source. A stability test should be done on the busbar relay same as the general differential relay. This is the testing of busbar protection.

This is all the concept of busbar protection. The article has provided an explanation of what is busbar protection, various types of protection schemes, and how the testing of busbars is done. With all these concepts, also consider a few examples of busbar protection.