What is the difference between measurement CT and protection CT?
Table of Contents
- 1 What is the difference between measurement CT and protection CT?
- 2 What is protective CT?
- 3 What will happen if we interchange protection CT with metering CT?
- 4 What is the class of CT?
- 5 Why CT secondary is short circuited?
- 6 How is CT VK calculated?
- 7 What is the difference between CT and CT for measurement and protection?
- 8 What is the difference between CT and metering CT?
What is the difference between measurement CT and protection CT?
Current transformers are used for both metering and protection purposes. 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.
Can we use a measuring CT for protection?
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. Similarly, a Metering Current Transformer should not be used for protection purpose.
What is protective CT?
A “protection” current transformer (CT) must saturate sufficiently high to allow a relatively accurate measurement of the fault current by the protection whose operating threshold can be very high. Current transformers are thus expected to have an Accuracy Limit Factor (ALF) that is usually fairly high.
What is a measuring CT?
CT Measurements The Current Transformer (CT) is used to sense AC current in single-phase or three-phase mains circuits. The CT typically has a 1A or 5A AC secondary that connects to a current, power or energy meter. This allows the meter to be located away from the mains wiring.
What will happen if we interchange protection CT with metering CT?
Metering current transformers are designed to be within quite accurate values up to say two x rated current, and down to <0.01 x rated. Consequently a protection relay connected to a metering current transformer will get a heavily saturated waveform during fault conditions and it won’t work properly.
What is VK in CT?
According IEC, Knee Point Voltage of a Current Transformer is defined as the voltage at which 10 \% increase in voltage of CT secondary results in 50 \% increase in secondary current.
What is the class of CT?
The class designation is an approximate measure of the CT’s accuracy. The ratio (primary to secondary current) error of a Class 1 CT is 1\% at rated current; the ratio error of a Class 0.5 CT is 0.5\% or less. Errors in phase are also important, especially in power measuring circuits.
How does a CT measure current?
The CT ratio is the ratio of primary current input to secondary current output at full load. For example, a CT with a ratio of 300:5 is rated for 300 primary amps at full load and will produce 5 amps of secondary current when 300 amps flow through the primary.
Why CT secondary is short circuited?
Very high voltages will result from open circuiting the secondary circuit of an energized current transformer so their terminals must be short-circuited if the ammeter is to be removed or when a CT is not in use before powering up the system.
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…
How is CT VK calculated?
Importance of Knee Point Voltage for PS class CT:
- Differential protection Scheme:
- CT Knee Point Voltage can be calculated using the formula;
- Related Article:
- Example:
- If the system fault current is 30 KA, CTR-600/5, RCT+RL+RR=0.5 Ohm.
- Vkp = K * If/CTR * (RCT + RL + RR)
- Vkp = 2*30000/120*0.5 =250 Volt.
- Test Set-up:
What are the errors in CT?
The ratio (primary to secondary current) error of a Class 1 CT is 1\% at rated current; the ratio error of a Class 0.5 CT is 0.5\% or less. Errors in phase are also important, especially in power measuring circuits. Each class has an allowable maximum phase error for a specified load impedance.
What is the difference between CT and CT for measurement and protection?
By reduce the power system primary current to lower value CT is used for measuring purpose.By permit the use of standard current rating for secondary equipment CT is used for Protection purpose.The CTs used for measurement and protection purposes have different properties.Following are the basic differences between two. 1.
What is a protective CT?
The Protective CT manages to push the (high) secondary current (short circuit current) through the load (connection cables, input CTs of the device or devices in series, it’s own CT resistance).
What is the difference between CT and metering CT?
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. Similarly, a Metering Current Transformer should not be used for protection purpose. Let the discuss the reason behind this.
Can protection class CT be used as metering CT?
Therefore, Protection class CT should not be used as Metering CT. Similarly, a Metering Current Transformer should not be used for protection purpose. Let the discuss the reason behind this. Why can’t we use Protection CT for Metering Purpose?