# What is differential protection CT?

## What is differential protection CT?

A differential protection monitors an area limited by CTs which measure incoming and outgoing currents. If the outgoing currents are not consistent with the incoming currents, this is normally because a fault has occurred in the protected area.

## What is generator differential protection?

1. Generator differential protection (87 G) It is unit type protection, covering the stator winding for phase to phase faults due to breakdown of insulation between stator phase windings.

How do I choose CT for differential protection?

These CTs are selected based on the amount of current they are expected to measure up to certain value of current, during fault conditions, in which they can measure without loss of accuracy. In their application to transformer differential protection, CTs are usually selected based on the full load rating of circuit.

### What is CT in generator?

I. INTRODUCTION. The IEEE Guide for the Application of Current Transformers Used for Protective Relaying Purposes recommends selecting identical current transformers (CTs) and burden impedances for differential relaying in generator protection applications [1].

### What is the difference between PS class and 5P20 CT?

the accuracy of PS class is not defined. generally used for unit protections differentials…. And a 5P20 CT means it will give a +_5% error when it reads 20 times the rated current …which means when a fault happens more than the CT ratting upto 20 times it can measure with a 5% errors with plus minus…

What is CT accuracy class 0.2 S?

An 0.2s accuracy class means that the measurement has an error rate of 0.2% over a range of 20 to 120% of the nominal current (In) and at a specific accuracy above 1% of In.

#### What is the difference between differential protection of transformer and generator?

Answer. There is no difference. Differential protection is differential protection. CTs around the 3 outputs of the generator are matched with CTs on each leg of the star point of the generator.

#### Why NGR is used in generator?

Neutral Grounding Resistors (NGR) protect power system generators and transformers by controlling the ground overcurrent and transient overvoltages [1]. Integrity and intactness of these apparatuses are necessary to prevent the system from being ungrounded or solidly grounded [2], [3].

How do you calculate generator CT ratio?

Calculate the CT ratio. The CT ratio is the inverse of the voltage ratio. In this example, the voltage ratio is 1:5, so the CT ratio is 5:1. This means the current level is stepped down 5 times where, if the primary current is 200 amps, the CT output is 40 amps.

## How CT is used for protection?

Protection CT A protection current transformer is designed to operate well into the overcurrent range. This enables the protective relays to measure fault currents accurately, even in very high current conditions.

## What is burden of CT and PT?

Burden of CT can be specified as Volt-Ampere absorbed at certain Power Factor i.e the VA that can be consumed by the load. The burden can also be expressed as total Impedance in terms of ohms connected on secondary of CT i.e. pilot conductor and instrument burden (I2 x R=VA).

Why PS class CT used for differential protection?

The PS class CTs used for differential protection have identical knee point voltage. Under through fault condition, both the CT operates, and thus the differential relay remains inoperative.

### Which is better 5P10 or 5P20?

Its application which differetiate the use of 5P10 and 5P20. If the breaker is used for backup protection say incommer etc you can use 5P20, but if it is say an incommer ACB/ MCCBof PMCC, you should use 5P10 only.

### What is the difference between 0.5 and 0.5 S Class CT?

Class 0.5s is more accurate when you got low values of current. For class 0.5s and with a current between 1-5% In, you got on class 0.5s a 0.75% error. For class 0.5 and with a current between 0-5% In, you got on class 0.5s a 1.5% error. For a current equal to In, they both got a 0.5% error.

What is the difference between Class 0.2 and 0.2 s?

0.2 and 0.2S refers to the accuracy of the Current Transformer. A 0.2S CT has a much higher accuracy than 0.2. Accuracy class of 0.2 means +/- 0.2 % error.

#### What are disadvantages of differential protection?

The differential scheme described suffers from the following drawbacks: Unmatched characteristics of CTs. Ratio change as a result of tapping. Magnetizing inrush current.

#### How much percentage of winding is protected by differential protection?

The percentage of winding to be protected against phase to ground fault is 85%.

Why NGR is not used in LV system?

Low Resistance Grounding is used for large electrical systems where there is a high investment in capital equipment or prolonged loss of service of equipment has a significant economic impact and it is not commonly used in low voltage systems because the limited ground fault current is too low to reliably operate …

## Why neutral grounding is required?

Importance of Neutral Grounding The neutral points of transformers, generators and rotating machinery to the earth ground network provides a reference point of zero volts. This protective measure offers many advantages over an ungrounded system, like: Reduced magnitude of transient over voltages.