Table of Contents
- 1 Why should a secondary circuit of a traditional CT always be shorted?
- 2 Why CT should not be open circuited?
- 3 What will happened when CT is energized in circuit breaker?
- 4 What is the difference between measuring CT and protection CT?
- 5 What happens if there is a short circuit?
- 6 Why do we short circuit a current transformer?
- 7 What are the standards for short circuit analysis?
Why should a secondary circuit of a traditional CT always be shorted?
CT secondary terminals should never be kept open. In normal condition, PT secondary is connected to some impedance offered by relay / measuring instrument. Therefore the current through the secondary circuit is low. This high current will lead to overheating and consequent damage to the PT.
Why CT should not be open circuited?
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. This results in the core being saturated through a large portion of the cycle.
What happens when a CT is open circuited?
If CT is kept open-circuited, no current will flow in the secondary, and consequently, no secondary flux will be set up in the core. In absence of secondary current, the net flux will be higher than the flux generated in the core when CT is connected to load.
What will happened when CT is energized in circuit breaker?
Exploding of the CT results in Power Interruption and consequently Loss of revenue. Also, the exploding CT may damage the nerby equipments, leading more Loss. Also, if someone accidently touches the Open Circuited CT Secondary, due to such High Voltage, he will get electrocuted and it may be a Fatal accident.
What is the difference between measuring 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.
Why CT secondary is 1A or 5a?
As the number of secondary turns in a CT with a 1A secondary current is more, so also will be the open circuit voltage of the CT secondary. Hence, the CT needs to be insulated for a higher voltage. This increases the insulation thickness and hence the size of the CT.
What happens if there is a short circuit?
A short circuit current can be very large. If unusually high currents exceed the capability of protective devices (fuses, circuit breakers, etc.) it can result in large, rapid releases of energy in the form of heat, intense magnetic fields, and even potentially as explosions known as an arc blast.
Why do we short circuit a current transformer?
Unless a burden (i.e. meters, relays, etc.) is connected to the CT, current transformers should always be shorted across the secondary terminals. The reason is very high voltages will be induced at the terminals. Think of the CT as a transformer, with a 1 turn primary and many turns on the secondary.
What are short circuit currents and what are they called?
Short-Circuit Currents are currents that introduce large amounts of destructive energy in the forms of heat and magnetic force into a power system. A short circuit is sometimes called a fault.
What are the standards for short circuit analysis?
NEC 110 requires that a short circuit analysis be done for all electrical equipment and panels. The two most common standards for short circuit current calculations are the ANSI/IEEE C37.010-1979 standard and the International Electro-technical Commission (IEC) 60909 standard.