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Sunday, September 11, 2011

Current Transformer Nameplate Data (Part 2)

I have posed before the commonly data on a current transformer nameplate. Listed below are the data and its brief description:

a. Current Transformer brand- The maker of the current transformer.

b. Type/model: Manufacturers are making current transformers of different sizes and specifications. A specific model usually have different available CT ratios, number of cores, height, etc to suit the customers' needs. The customer can state the type/model when inquiring to the company for aftersales support and ordering replacement or spare current transformers.

c. Serial number- As the name implies, this is the batch number of the product. This number is used to check if the ordered items are the ones delivered at your end. The serial number is also used to identify a particular equipment on the factory test reports so, the product which were tested and passed the limiting criteria can be verified as the items delivered.

d. Year- This is the manufacturing year of the current transformers. Most high voltage power equipment have a specific lifespan and this is usually given as the useful age of the equipment. So, we can actually see if the equipments at our substation are already nearing its useful age so that we can already plan when these equipments are needed to be replaced.

e.Rated voltage Level- this is the nominal or normal level of voltage in which the equipment is designed for use.

f. Thermic nominal short time current- This is the value of overcurrent that the current transformer can carry without breakdown for a short period of time (1 second).

g. Rated frequency- The frequency at which the current transformer is recommended for use.

h. Weight- Usually in kg; this is useful in the design of the pedestal to be used for each unit of the current transformer.

i. Peak withstand current- This is the value of current on which the current transformer can carry instantaneously or momentarily during short circuit fault.

j. Rated primary current- This is the nominal or normal current that the equipment is designed to carry.

k. CT ratio: This are the available ratios that the meters and relays can use. The actual current passing through the current transformer cannot be used directly by the relays and meters. The ratios available are used to transform these current into usable values applicable to the meters and relays.

l. CT core: These are the available cores dedicated for a single relay or meter. Each meter or relay has to use at least one core for a set of CT. So, if there are one relay and one meter to be connected at the CT, then there must be at least two CT cores of that CT.

m. VA-This is the burden per CT ratio. The burden being referred is used to compute for the impedance of the CT ratio to be used. The impedance is needed so that the readings on meter or relay can be adjusted accordingly so that it will measure accurate value. So, the effect of the impedance will be eliminated from the readings of the relay or meter connected.

n.Class- This is used to determined whether the ratio available is intended for protection or metering. Ratio for protection has the letter P on its class while for metering, the letter B is indicated for burden. Sometimes, the VA is not given but there is a table of burdens for a particular class. For metering, the burden must be as low as possible so that the reading will be accurate while for metering, the CT saturation must be as high as possible so that the relay can operate precisely upon the pickup of overcurrent.

1 comment:

  1. Narayan Powertech explosions of the transformers! http://lmh-trade.ee/


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