Skip to main content

CURRENT TRANSFORMERS ROUTINE TEST PROCEDURE

CURRENT TRANSFORMERS ROUTINE TEST PROCEDURE
C57.13.5 Test procedures for current transformers.

Inter-turn overvoltage test
The test shall be performed in accordance with one of the following procedures. If there is no agreement between the manufacturer and user, the choice of the procedure shall be left to the manufacturer. If secondary protective devices are provided, these devices shall be installed for the inter-turn overvoltage test.

Procedure A
With the secondary windings open-circuited (or connected to a high impedance device which reads the peak
voltage), a substantially sinusoidal current shall be applied to the primary winding. The test current shall be increased until one of the following conditions is reached:

   a) The r.m.s. value of the applied current is equal to the maximum primary current corresponding to the continuous thermal current rating factor (RF), or
   b) The peak value of the secondary induced voltage is equal to:
      1) 280 V for metering rated current transformers, or
      2) 2.8 times the secondary terminal voltage rating for relaying rated current transformers

The test shall be maintained for 60 s.

Procedure B
With the primary winding open-circuited, a test voltage (at an elevated frequency not exceeding 400 Hz) shall be impressed to the terminals of each secondary winding. Both the test voltage and frequency shall be increased until one of the following conditions has been reached:

   a) The peak value of the applied secondary test voltage is equal to:
      1) 280 V for metering rated current transformers, or
      2) 2.8 times the secondary terminal voltage rating for relaying rated current transformers
Or,
   b) The r.m.s. value of the secondary current is equal to the continuous thermal current rating factor (RF)

The test duration shall be in accordance with 4.1.8.

At the frequency of 400 Hz, if the voltage achieved with the secondary current value corresponding to the continuous thermal current RF is lower than the value provided in a) above, then the voltage obtained shall be regarded as the test voltage.

The gas pressure of the gas-filled transformer may be at any setting equal to or less than the pressure given in Clause 5 for the test.

The transformer shall be considered as having met the requirements if no external or internal disruptive discharge or collapse of voltage is observed, and, if provided, the secondary protective devices remain inoperative during the test.

Accuracy test for the metering rated current transformers
  • The test shall be performed in accordance with 6.11 and 8.1 of IEEE Std C57.13-1993.
  • The calibration of the test system provided in 4.3 shall apply.
  • The current transformer shall be demagnetized in accordance with 8.2 of IEEE Std C57.13-1993 before the accuracy test.
  • The gas pressure of the gas-filled transformer may be at any setting for the test.
  • The transformer shall be considered as having met the requirements if the performance is within the limits of the accuracy class.

Resistance measurement of relaying rated secondary windings
The resistance of relaying rated windings including tap portions shall be measured in accordance with 8.5 of
IEEE Std C57.13-1993. The measured value shall be corrected to 75 °C.

The gas pressure of the gas-filled transformer may be at any setting for the test.

The resistance data obtained shall be compared with the design values to ensure proper construction.

Performance characteristics of relaying rated current transformers
The test comprises the following:

   a) With the primary winding open-circuited as shown in Figure 5, a substantially sinusoidal voltage equal to the secondary terminal voltage rating, corrected with the additional voltage due to the winding resistance voltage drop, shall be applied to the full secondary winding. The excitation current expressed as a percentage of the 20 times the rated secondary current shall be recorded.
   b) The short-circuit impedance of the lowest tapped portion of the secondary winding shall be measured in accordance with item a) of 8.3.1.2 of IEEE Std C57.13-1993.
   c) The turns-ratios of the secondary winding and the tapped portions to the primary winding shall be measured.

The gas pressure of the gas-filled transformer may be at any setting for the test.

The transformer shall be considered as having acceptable performance characteristics if:

   1) The percent excitation current is not higher than 10%,
   2) The short-circuit impedance is not higher than 1.05 times the resistance of the lowest tapped portion of the measured secondary winding,19 and
   3) The turns-ratios are in accordance with the marked ratios.

source: C57.13.5 IEEE Trial-Use Standard of Performance and Test Requirements for Instrument Transformers of a Nominal System Voltage of 115 kV and Above
Labels:

Comments

  1. Miracle ElectronicsOctober 4, 2016 at 5:45 PM

    Unlike a voltage transformer, the primary current of a current transformer is not dependent of the secondary load current but instead is controlled by an external load. The secondary current is usually rated at a standard 1 Ampere or 5 Amperes for larger primary current ratings.
    Power Transformers in India | Wire Harness Manufacturer in India

    ReplyDelete

Post a Comment

Popular posts from this blog

PARTS OF A POWER TRANSFORMER

What are the name of the basic parts of a Power Transformer? We can not deny the fact that only a handful of electrical engineering students are presently familiar with power transformers especially on what it looks like. Unlike a transformer we found in our homes, a power transformer’s appearance and construction is somewhat more complicated. It is not just a simple winding with a primary and secondary terminal although basically any transformer has one. The function that a power transformer plays in an electrical system is very important that an electric utility can not afford to loss it during its operation. Our discussion here will focus more on the basic parts and functions of a power transformer that are usually tangible whenever you go to a substation . Although not all power transformers are identical, nonetheless they all have the following listed parts in which the way of construction may differ.
48 comments
click here to continue

ELECTRIC MOTOR FRAME SIZE STANDARD SPECIFICATIONS

ELECTRIC MOTOR FRAME SIZE STANDARD SPECIFICATIONS How is electric motor frame size being specified? Motor frame dimensions have been standardized with a uniform frame size numbering system. This system was developed by NEMA and specific frame sizes have been assigned to standard motor ratings based on enclosure, horsepower and speed. The current standardized frames for integral horsepower induction motors ranges from 143T to 445T. These standards cover most motors in the range of one through two hundred horsepower. Typical example of where you can locate the frame is shown in Fig 1.2.D – Frame No. The numbers used to designate frame sizes have specific meanings based on the physical size of the motor. Some digits are related to the motor shaft height and the remaining digit or digits relate to the length of the motor. The rerate, or frame size reduction programs were brought about by advancements in motor technology relating mainly to higher temperature ratings of insulating mate
5 comments
click here to continue

ELECTRIC MOTOR NAMEPLATE SPECIFICATIONS

How do we interpret an electric motor nameplate? Motor standards are established on a country by country basis.Fortunately though, the standards can be grouped into two major categories: NEMA and IEC (and its derivatives). In North America, the National Electric Manufacturers Association (NEMA) sets motor standards, including what should go on the nameplate (NEMA Standard MG 1-10.40 "Nameplate Marking for Medium Single-Phase and Polyphase Induction Motors").
40 comments
click here to continue