What is Relay burden?
Re: relay burden As we know, burden in current transformer terminology is the load connected to the secondary terminals and is expressed either as VA (volt-ampere) and power factor at a specified value of current, or as total ohms impedance with the effective resistance and reactive components.
What is CT metering?
Metering CT: The ratio of a 0.3B0. 1 rated Metering CT is accurate to 0.3 percent if the connected secondary burden if impedance does not exceed 0.1 ohms. A 0.6B8 rated metering-class CT will operate within 0.6 percent accuracy if the secondary burden does not exceed 8.0 ohms.
What is PS class CT?
PS Class CT is also known as PX Class or simply Class X Current Transformer. It is special type of current transformer meant for protection purpose. Deviation in characteristics of CTs may lead to spill current in the secondary and even lead to actuation of protection element even under through fault condition.
Can we use protection CT for metering?
Protection Current Transformer (CT) and Metering CT are two different types of CT as per their requirement and hence design. Therefore, Protection class CT should not be used as Metering CT.
Why CT secondary is shorted?
A CT has generally 1:1000 or 1:2000 primary:secondary ratio. Now if secondary of CT is left open then a extremely high voltage will appear across open secondary ends which might damage CT. Therefore secondary is intentionally shorted when output is not connected to any measuring instrument.
How CT is used for protection?
A Current Transformer (CT) is used to measure the current of another circuit. CTs are used worldwide to monitor high-voltage lines across national power grids. A CT is designed to produce an alternating current in its secondary winding that is proportional to the current that it is measuring in its primary.
What is difference between metering and protection?
By reduce the power system primary current to lower value CT is used for measuring or metering purpose. By permit the use of standard current rating for secondary equipment CT is used for Protection purpose.
What is knee point voltage?
The knee point is defined as the voltage at which a 10% increase in applied voltage increases the magnetizing current by 50%. For voltages greater than the knee point, the magnetizing current increases considerably even for small increments in voltage across the secondary terminals.
What is Wire Pilot?
A wire is connected between the CT which is located in different ends of the protection. zone. This wire provide the path for the circulating current produce in abnormal condition, which is sensed by the realy and therefore is tripped, this wire thus used is known as pilot wire. 10.3K views.
What is 5P10 class CT?
5P10 means the maximum permissible limit of error (accuracy limit) is 5% at 10 times rated current (Accuracy Limit Factor). CT will give ratio error of only 5% even if fault current reaches 10 times the nominal value (In), after that CT will start to saturate.
What is 0.2 S Class CT?
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 does the number 5P20 mean on a CT?
5p20 means that. there will be error of 5% when the primary current is 20 times. For example, if. the ct is 1000/1 , then in case of fault, when the fault current is 20000 A, then.
What is ISF CT?
ISF or instrument security factor of current transformer is defined as the ratio of instrument limit primary current to the rated primary current. The instrument limit primary current of metering CT is the value primary current beyond which CT core becomes saturated.
Why the secondary of CT should not be open?
If the primary circuit has current flowing the secondary circuit should never be opened. This can cause very high voltages to occur due to the Ampere-Turns of the primary that start magnetizing the core. While it is acting as a transformer it will cause very high voltage peaks. …
Why CT burden is important?
Higher burden selection against the required burden results in CT measurement inaccuracy. Thus, if a CT designed for 15 VA burden is operated for 5 VA, there will be higher error in its measurement even when the CT is operating at its rated current. Thus, it is very important to select a CT with appropriate burden.
What happens when CT is saturated?
In saturation, there is no flux change when the primary current changes (as the core is already carrying maximum flux). Since there is no flux change there is no secondary current flow. Therefore in saturation, all of the ratio current is used as magnetizing current and none flows in to the load connected to the CT.
What can be done to avoid CT saturation?
The only way to remove this remanence is by degaussing the CT. Degaussing can be done by applying primary rated current and a variable load to the CT secondary terminals. Start the load at a high resistance to cause the CT to saturate in both the positive and negative directions.
How can you prevent CT saturation?
Avoid Current Transformer Saturation Using Adjustable Switched Resistor Demagnetization Method. Abstract: In some conditions, the flux in the core of current transformers (CT) increases. If this increase in flux leads to saturation of the protective core, it can create a lot of problems in power system protection.