Current transformer polarity test

Polarity test of transformer assume, we want to determine the polarity of 22012 v transformer. Ip test is conducted especially to determine the dryness and cleanliness of the insulation. The output current from the ct comes from one terminal and the same amount if current return to the same ct after circulating the other electrical devices. This type of current transformer tests is usually carried out during the primary injection tests described in 8. The current transformer ct polarity markings are shown in figure 2. Megger is passionate about and delivers on safety, accuracy, efficiency and usability of our transformer test instruments. Polarity test of transformer polarity means the direction of the induced voltages in the primary and the secondary winding of the transformer. Megger relay and current transformer test set the voltage present on the primary winding would be 1 volt. A typical polarity test kit schematic is given atop the next column. Confirm the polarity recorded with the one shown in drawings. This can be done during polarity test, by shorting all other cores at the ct secondary terminals while checking the. The cpol2 can be used as an accessory for several omicron test sets.

In case of multi core current transformers, it has to be confirmed that the correct core is connected to the correct circuit. You can verify the polarity of a ct in the field with a 9v battery, using the following test procedure. A current transformer test set identifies potentially disastrous current transformer faults, preventing the primary current from overwhelming insulation and in effect causing windings to short circuit. This test is important for the calculation of transformer winding heat losses used for winding temperature testing, and as base data for future assessment in the field.

We are persistent innovators with a deep understanding of transformers and their testing, striving to. Similar polarity ends of the two windings of a transformer are those ends that acquire simultaneously positive or negative polarity of emfs induced in them. Correct operation of mps and fps relays depends on accurate polarity. The ctt1 is a microprocessorbased current transformer tester that measures ct excitation current, turns ratio, and winding polarity tests, all without having to switch the leads during testing. Knee point voltage and magnetization curve have to be tested by using current transformer test kit mct. The mct1605 has a large display, permitting the user to easily read all pertinent data while the test is being performed and providing the ability to view the current transformers saturation curve. Introducing the ctvt45 instrument transformer test set, a multifunction tester designed to test all types of current transformers and voltage transformers. A knowledge of polarity is also required to connect potential and current transformers to power metering devices and protective relays. Current transformer polarity test cr4 discussion thread. Markings on current transformers have been occasionally misapplied by the factory. It offers the following functionalities and features. The convention is that current entering a transformer at the end of a winding marked with a dot, will tend to produce current exiting other windings at their dotted ends.

Although includes 5 low side taps and 1 high side tap. Maintaining proper polarity is important in power system protection, measurement and control systems. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the. Polarity check of current transformers and voltage transformers cts and vts polarity check of terminals and wiring connected to cts and vts.

With one click following test can be performed such as polarity etc. I am je of nagbhir sub station of 225 kv newly electrified section and testing started of current transformer when test ct ratio by injecting current in primary bushing of old ct which was 20 years old ct installed in circuit,after testing values not found according to ratio,100 amps inject and found in secondary terminal 3. Polarity all current transformers are subtractive polarity. Thansk for a2a after all, a transformer is nothing more than a set of magneticallylinked inductors, and inductors dont usually come with polarity markings of any kind if we were to look at an unmarked transformer, we would have no way of knowing. With model cter91 current transformers can be tested while mounted in transformers, oil circuit breakers breakers or switchgear without moving bushings and cts. Connect one end of the long trailing lead to the outgoing terminal of the circuit mcb. Using the voltagecomparison method, model cter91 provides a variablevoltage output up to volts and precision instrumentation for testing single and multiratio cts. If the two transformers are connected in parallel, then the polarity should be known for the proper connection of the transformer. Rental units instock and available for immediate shipping at atec. Testing and commissioning requirements for switchgear. Burden the load on an instrument transformer is referred to as a burden. Current transformers cts are used to supply a proportional current to the current input of metering and relaying equipment. Note down the transformer ratings as well as the turn ration if accessible. Current transformer saturation, ratio and polarity test.

There are two types of polarity one is additive, and another is subtractive. Polarity all instrument transformers are subtractive polarity. Main keywords and important concept point for this articles are transformer testing, what is current transformer, ct test, primary injection test. Current flows from high voltage point to low voltage point due to the potential difference between them. Back to the basics current transformer ct testing as test equipment becomes more sophisticated with better features and accuracy, we risk turning our field personnel into test set operators instead of skilled field service technicians. In a balanced 3phase, deltaconnected system, the line current is equal to blank. Furthermore, any queries on the topic of the polarity test please get back to us by commenting in the comment section below. Just like a battery, a current transformer too has a polarity. A wide variety of polarity test of current transformer options are.

A test set operator connects the leads, pushes the buttons, and records the. Ct test and current transformer test procedure with testing. Why polarity testing of transformer is needed answers. In insulation resistance test, a high dc voltage is. T polarity tester ct polarity tester manufacturer from.

Verifying the polarity of a transformer can be accomplished with a simple voltage test using the following steps. The polarity marks on a ct designate, the relative instantaneous directions of the current i. It may be determined by a simple voltage measurement, as follows. What method is used to test for polarity and check transformer lead markings. We use additive polarity for smallscale distribution transformers and subtractive polarity for largescale transformers. Understanding polarity is essential to properly paralleling singlephase transformers and connecting instrument transformers current and potential to metering devices and protective relays.

Testing ct ratio by voltage method, having fast response time, high precision and reliability. A transformer can be used on a threephase supply by using a threelegged core with primary and secondary windings on each leg, as shown in figure 5. Polarization index test pi value test along with insulation resistance test ir value test is conducted on hv electrical machine to determine service condition of the insulation. Transformer polarity test it is unusual for a line crew to need to conduct a polarity test, since polarity is confirmed on nameplates. It has always been a challenge to explain transformer polarity in a manner easily understood by students.

The polarity of current transformers is extremely important. Perform a polarity test of each current transformer. The mct provides a microprocessor controlled variable voltage output and. Electrical polarity simply describes the direction of the current flow. This test is considered as one of the main test, its aimed to test. For the parallel operation of the transformer, the polarity of the transformer windings must be known i,e both primary. In this article basics of transformer polarity is discussed. We hope that you have got a basic idea about this concept.

It is a lightweight, rugged, userfriendly test set that performs basic and routine testing of cts and vts pts. Significance of polarity in current transformers electrical india. An understanding of polarity is also required to connect potential and current transformers to power metering and protective relays. Transformer polarity copyright 2002 kilowatt classroom, llc.

Particular care must be taken in case of special schemes like bus differential. The polarity test diagram of transformer circuit is shown above. Winding resistance test measures ct winding resistance with the injection of a test. Polarity marks show the connections where the input and output voltages have the same instantaneous polarity, this is important when hooking up current transformers for relay protection and metering.

There are 2 generally accepted methods of testing a cts polarity using simple meters and connections. The ratio of the readings of the ammeters in the primary and secondary circuit of the ct under test is taken which should approximate to the ratio marked on the ct. P1 p2 in a current transformer cr4 discussion thread. For bus couplers, if cts are installed in these feeders, consult engineering team for proper orientation of p1p2 of the cts. Polarity of transformer windings your electrical guide. Current transformer is used to sense the primary line current. What is polarity and why its important for transformers. Note that the direction of the secondary current is the same, independent of whether the. Current transformer polarity check using a battery and meter. Understanding transformer polarity electrical academia.

Unanswered questions what are the different hardware that will be needed by producer of the voice mail the srvice provider and the beneficiary. A ct under test is assumed to have correct polarity if instantaneous current direction for primary and secondary current is opposite to each other. The importance of the polarity test is that by knowing the polarity of different windings we can be able to avoid shortcircuits while parallelly operating the transformers to meet peak demands, the transformers are connected in parallel to operate. Disconnect all power prior to testing and connect an analog voltmeter to the secondary terminal of the ct to be tested. Polarity refers to the instantaneous direction of the primary current with respect to the secondary current and is determined by the way the transformer leads are brought out of the case. There are four different ways in which single phase transformers can be connected to form three phase banks. Current transformers testing and commissioning guidelines.

Megger relay and current transformer test set mrct megger. More specifically, if 120 volts were applied to the secondary of a 600. These are indicated by the dot convention as illustrated already. Testing polarity in lightning circuit and transformer test of polarity of lighting circuits this test must be done with the supply disconnected and may be carried out as follows. In subtractive polarity, if v c v a v b, it is a stepdown transformer and if v c v b v a, it is a stepup transformer. Transformer polarity depends on whether the coils are wound around the core clockwise or counterclockwise, and how the leads are connected. The prime is a new high current microohmeter of smc, which can be used for measuring the secondary resistance of current transformer winding, provided that the measured resistance is less than 1 ohm, and also as a general purpose contact resistance test set for any connection test of the current transformer secondary circuits. What is a polarity test importance, methods used to test. Dear, a person who know the words current transformer, polarity, injection etc should have the ability to find out little further, so he can find the answer himself. Current transformers can be tested in their equipment configuration, such as being mounted in transformers, oil circuit breakers or switchgear.