What is the purpose of differential protection?

What is the purpose of differential protection?

One of the most important protection in power system is differential protection. It is used to protect the electrical equipment against internal fault such as internal winding short circuit or bus bar phase to phase short circuit, inter turn short, winding puncture etc.

Why do we need bias in differential protection?

The purpose of biased differential protection is to detect faults with high selectivity and sensitivity. This means that it can trip with no intentional time delay for faults within its zone of protection, the reason why differential protection is often applied on high value equipment such as transformers.

What is the principle of differential protection?

Principle of differential protection Differential protection is based on the fact that any fault within an electrical equipment would cause the current entering it, to be different, from the current leaving it.

Which relay is used in differential protection?

Voltage Balance Differential Relay For the protection of the feeders, the voltage balance differential relays are used. The voltage differential relay uses two similar current transformer places across the protective zone with the help of pilot wire.

What class of CT is preferable for differential protection?

For differential protection, we use class PS CT’s on both sides of equipments(suppose for a transformer). If i know that Maximum Fault Current(under Worst case) that will flow through transformer is 12 times the rated current, then i can use CT’s with class: 5P15 or 5P20.

What is percentage differential protection?

The percentage differential relay is designed to operate the differential current in terms of its fractional relation with actual current flowing through the circuit. It is used to protect the system under Current transformer saturation, unequal CT ratios, nuisance trip etc.

Why it is called percentage differential relay?

During fault condition…the operating force become higher than the restraining force, due to this the operating coil trips the mechanism. Thus the ratio of differential current to average restraining current is always a fixed percentage. Therefor it is called as percentage differential relay.

Why is it superior to simple differential protection?

Why biased differential protection is preferred over simple differential protection? Biased differential relay is preferred because its operation is not affected by the trouble arising out of the difference in the CTs ratios for high values of external short circuit currents.

Why do we need protection at input side?

All equipment installed in a power electrical system have standardized ratings for short-time withstand current and short duration power frequency voltage. The role of the protections is to ensure that these withstand limits can never be exceeded, therefore clearing the faults as fast as possible.

What is a 52 relay?

52 AC circuit breaker A device that is used to close and interrupt an AC power circuit under normal conditions or to interrupt this circuit under fault or emergency conditions. 55 Power factor relay A relay that operates when the power factor in an AC circuit rises above or falls below a predetermined value.

What is RCT in CT?

Lm is the saturable magnetisation inductance, L is secondary of an ideal current transformer, RCT is resistance of the CT secondary winding, RW is resistance of wiring and RL is the burden i.e. the protection relay.

When to use a stabilizing resistor in high impedance differential protection?

Stabilizing Resistor in High Impedance Differential Protection is used to prevent the operation of Relay in case of through fault. Through fault is a fault outside the zone of protection. Lets us assume that High Impedance Differential protection is used to protect a Bus bar as shown in figure.

When to use Ref or differential fault protection?

As Differential Protection initial setting is usually around 20 percent to avoid CT Errors and all. So if the fault current is below 20 percent it can’t provide protection even for the internal faults. So we are using REF protection with lower setting usually around 5 to 10 percent.

What are the advantages of differential protection of transformer?

The Differential Protection of Transformer has many advantages over other schemes of protection. The faults occur in the transformer inside the insulating oil can be detected by Buchholz relay.

Where are the resistors in a differential line receiver?

In the above diagram of a differential line receiver for an encoder, resistors are place between each line and its inverse. I don’t see how this would lower the current of each line, so I assume it… Stack Exchange Network