In the electrical field, CT and PT stand for Current Transformer (CT) and Potential Transformer (PT) respectively. Capacitor Voltage Transformer (CVT) is abbreviated as CVT.

Current Transformer (CT)

CT is a device used to measure large currents. It is able to convert high current values into lower standard current values (usually 5 amps or 1 amp) for easy measurement and protection of circuits. CT is widely used in power systems for functions such as current measurement, overload protection, and ground fault detection.

Potential Transformer (PT)

PT is used to measure high voltage and convert it into lower standard voltage values (usually 100 volts or 110 volts). It is mainly used in voltage measurement, energy metering, and protection relays. PT ensures safe and accurate monitoring of the status of high voltage circuits in low voltage environments.

Capacitor voltage transformer (CVT)

Capacitor voltage transformer (CVT) is a voltage transformer that is divided by series capacitors and then reduced and isolated by electromagnetic transformers. It is used as a meter, relay protection, etc. Capacitor voltage transformer can also couple the carrier frequency to the transmission line for long-distance communication, remote measurement, selective line high-frequency protection, remote control, teletypewriting, etc. Therefore, compared with conventional electromagnetic voltage transformers, capacitor voltage transformers can prevent ferromagnetic resonance caused by saturation of the voltage transformer core, and have many advantages in economy and safety.

Capacitor voltage transformers are mainly composed of capacitor voltage dividers and medium-voltage transformers. The capacitor voltage divider consists of a porcelain sleeve and several series capacitors installed in it. The porcelain sleeve is filled with insulating oil that maintains a positive pressure of 0.1MPa, and a steel bellows is used to balance different environments to maintain oil pressure. The capacitor voltage divider can be used as a coupling capacitor to connect the carrier device. The medium voltage transformer consists of a transformer, a compensating reactor, a lightning arrester and a damping device installed in a sealed oil tank. The space on the top of the oil tank is filled with nitrogen. The primary winding is divided into a main winding and a fine-tuning winding. A low-loss reactor is connected in series between the primary side and the primary winding. Since the nonlinear impedance and inherent capacitance of the capacitive voltage transformer sometimes cause ferromagnetic resonance in the capacitive voltage transformer, a damping device is used to suppress the resonance. The damping device consists of a resistor and a reactor, which is connected across the secondary winding. Under normal circumstances, the damping device has a high impedance. When the ferromagnetic resonance causes overvoltage, before the medium voltage transformer is affected, the reactor has been saturated and only the resistance load is left, so that the oscillation energy is quickly reduced.

Transformation ratio analysis

PT and CVT are voltage transformers, which are used to convert high voltage into low voltage. The secondary side is generally 100V, such as 10KVPT is 10KV/100V. The secondary side of PT cannot be short-circuited; CT is a current transformer, which converts large current into small current, generally 5A or 1A. The secondary side of CT cannot be open. Whether it is an electromagnetic or capacitive voltage transformer, it converts high voltage into low voltage for measurement, control, and protection systems. From the working principle, it is a small (small capacity) transformer, or it is better to call the equipment according to the standard name. Especially in the power operation department.

Working principle and composition details

The voltage transformer is actually a transformer with an iron core. It is mainly composed of primary and secondary coils, iron core and insulation. When a voltage U1 is applied to the primary winding, a magnetic flux φ is generated in the iron core. According to the law of electromagnetic induction, a secondary voltage U2 is generated in the secondary winding. Changing the number of turns of the primary or secondary winding can produce different ratios of primary voltage to secondary voltage, which can form voltage transformers with different ratios. The voltage transformer converts high voltage into low voltage in proportion, that is, 100V. The primary side of the voltage transformer is connected to the primary system, and the secondary side is connected to measuring instruments, relay protection, etc.; it is mainly electromagnetic (capacitive voltage transformer is widely used), and there are non-electromagnetic types, such as electronic and photoelectric types. CT-current transformer, spelled Current Transformer in English, is a conversion device that converts the large current on the primary side into a rated current of 5A or 1A suitable for use by instruments or relays. The current transformer consists of a closed iron core and a winding. Its function is to convert a large primary current into a smaller secondary current through a certain transformation ratio for protection, measurement, etc. For example, a current transformer with a transformation ratio of 400/5 can convert an actual current of 400A into a current of 5A.

How to use DEMIKS transformer dielectric loss factor tester

Preparation before testing

1. Check whether the appearance of the tester is damaged and whether the components are firmly connected.

2. Ensure that the power supply of the tester is normal and select the appropriate power supply method according to the on-site power supply conditions.

3. Fully discharge the transformer to be tested to ensure safety, and reliably isolate the transformer's tested winding from other windings and the ground.

4. Clean the test terminals of the transformer and remove impurities such as oil and dust on the surface to ensure good test contact.

Connect the tester

1. Connect the high-voltage lead of the tester to the high-voltage end of the transformer's tested winding, ensuring that the connection is firm and the contact is good.

2. Connect the test lead of the tester to the low-voltage end or neutral point of the transformer's tested winding, and reliably ground the ground lead of the tester.

Parameter setting of transformer dielectric loss factor tester

1. Set the corresponding test voltage, test frequency and other parameters on the tester according to the voltage level, capacity and other parameters of the transformer to be tested. In general, the test voltage should be selected according to relevant standards or test requirements, and the test frequency is usually 50Hz or other specific frequencies.

2. Set other parameters of the tester, such as measurement range, accuracy, etc., to ensure that the settings of the tester match the actual situation of the transformer being tested.

Test the dielectric loss factor of the transformer

1. After confirming that the connection and parameter settings of the tester are correct, start the tester and start the test. The tester will automatically apply the test voltage and measure parameters such as the dielectric loss factor and capacitance of the transformer.

2. During the test, pay attention to the display data and status of the tester to ensure that the test process is normal. If there is an abnormal situation, such as the tester alarm, data abnormality, etc., the test should be stopped immediately, the cause should be found and the fault should be eliminated before retesting.

Post-test processing

1. After the test is completed, turn off the power of the tester, wait for the high-voltage output of the tester to completely disappear, and then remove the test lead.

2. Record and analyze the test data to determine whether the insulation condition of the transformer is good. If the dielectric loss factor exceeds the range specified by the standard, the cause should be further analyzed and the transformer should be further inspected and tested if necessary.

3. Clean up the test site and keep the tester and test tools properly for next use.

The specific operation of transformer dielectric loss factor testers (also called as Transformer Tand Delta Tester) of different models and manufacturers may vary. When using, you should read the instruction manual of the tester in detail and test in strict accordance with relevant standards and operating procedures. If you need, you can consult the sales staff of Shanghai Demix Electric Technology. For more power test equipment, please visit the website: www.electrichv.com

The dry-type power frequency AC/DC test transformer is a transformer made of advanced technology and new materials using coil epoxy vacuum casting and CD-type iron core. It is mainly used for on-site detection of power systems and insulation performance tests of various electrical equipment. Its core features are that compared with the oil-immersed test transformers of the same capacity and voltage, it has the advantages of light weight, small size, beautiful appearance, stable performance, easy to use and carry, and no oil leakage. It effectively weakens the leakage magnetic field and improves the insulation strength and moisture resistance. It is particularly suitable for power systems and various power users to test the insulation performance, DC withstand voltage and leakage current of various electrical equipment on site. It is the preferred product to replace bulky oil-immersed transformers.

Working principle

The working principle of the dry-type power frequency AC/DC test transformer is based on the principle of electromagnetic induction. After the input voltage is adjusted by the control box, it is input into the primary winding (low voltage) of the transformer, and the electromagnetic induction principle is used to generate the same multiple of the output high voltage in the secondary winding (high voltage). When conducting DC withstand voltage and leakage current tests, you only need to install a high-voltage silicon stack at the high-voltage output end to obtain DC high voltage.

‌Beautiful appearance‌: The design focuses on aesthetics and is suitable for use in various environments.

‌Stable performance‌: The use of advanced production technology and new materials has improved insulation strength and moisture resistance, weakened magnetic leakage, and enhanced the stability and reliability of the transformer.

‌Easy to use‌: The wiring is simple and intuitive, the operation is convenient, and it is suitable for on-site operation.

Application scenarios

Dry-type AC/DC test transformers are particularly suitable for power systems and power users to test the insulation performance, DC withstand voltage and leakage current of various electrical equipment on site. It is an ideal choice to replace traditional oil-immersed transformers and is widely used in various high-voltage test occasions.

Instructions for use

1. Before use, you must read the instruction manual of the transformer and the instruction manual of the console that comes with it in detail. Connect the connection wires according to the instructions, and the ground wire should be well grounded.

2. The power supply of the dry-type transformer control box (station) is AC 220V and 380V, which are output to the low-voltage input terminal of the transformer through the voltage regulator. After the ratio output, it can be continuously adjusted to the rated voltage value.

3. Considering the safety of dry-type test transformers and the rigor of high-voltage tests, to avoid damage to equipment or test products, our factory can provide complete sets of equipment to meet users:

The complete set of equipment includes: high-voltage test transformers, transformer control boxes, voltage dividers, ball gap protectors, discharge rods, high-voltage oil cups, high-voltage silicon stacks (for DC tests), and digital microammeters (for DC tests).

4. When doing DC withstand voltage or leakage current test, you can first connect the high-voltage silicon stack and microammeter to the high-voltage output end of the high-voltage test transformer, and then gradually increase the voltage to conduct DC test.

5. When two test transformers are connected in series, the rated output voltages of the first and second transformers are equal, and the capacity ratio is 2:1. The second transformer must be placed on an insulating bracket to ensure insulation from the ground. When connecting in series, pay attention to the markings on the transformer (see the wiring diagram) to ensure that the polarity is connected correctly to ensure the output of the predetermined voltage, otherwise, the output voltage is zero.

Note:

① If A and B are connected in reverse. It will cause the high-voltage output to be zero (T1+T2=0), just swap A and B.

② The T2 test transformer chassis must be connected to the tray of the insulating bracket.

Dry-type test transformers strictly implement the regulations of the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China, and follow the standards of the power department and the Technical Supervision Bureau to ensure product safety.

The main products of Shanghai Demiks Power Technology Co., Ltd. include: "Series resonance test equipment, partial discharge test system, high voltage insulation withstand voltage, transformer test, circuit breaker test, relay protection, secondary circuit test, cable line test, lightning arrester insulator tester, SF6 test, oil test, DC system battery test, reactive power compensation generator detection, ground insulation resistance test, power metering test, etc." More than 200 products in 20 categories".

Choose Demiks for electic power safety! Contact email contact@demikspower.com

Power frequency withstand voltage test devices are widely used in electrical manufacturing departments, power operation departments, scientific research units and colleges and universities. Power frequency withstand voltage test devices are divided into two categories: integrated devices (below 30kV) and split devices. The console is composed of a contact voltage regulator (electric column voltage regulator for 50kVA and above) and its control, protection, measurement and signal circuits. It is connected to the 220V or 380V power frequency power supply, adjusts the voltage regulator (that is, the input voltage of the test transformer), and connects to the primary winding of the high-voltage test transformer to obtain the required test high voltage value according to the principle of electromagnetic induction. According to the test procedures, various large power transformers, power cables, steam turbines and hydro-turbine generators and other capacitive equipment must be strictly and regularly subjected to AC withstand voltage tests.

Insulation withstand voltage tests are divided into DC withstand voltage tests and AC withstand voltage tests. In the past, DC withstand voltage tests were used when conducting cable withstand voltage tests. Research and practice have shown that DC withstand voltage tests are ineffective and harmful to rubber and plastic insulation. China began to study and practice AC withstand voltage test technology in the 1990s. After more than 20 years of research and practice, countries around the world have adopted AC withstand voltage test instead of DC withstand voltage test. Relevant standard organizations at home and abroad have also made changes and revisions to the test methods of high-voltage cables. In May 1997, the CIGRI International Large Power Grid Working Conference questioned the DC withstand voltage test method adopted, and recommended the use of AC test methods at power frequency and near-power frequency (30-300HZ) for promotion and application worldwide. In provinces where China's power grid is relatively developed, AC withstand voltage test has become a mandatory standard. Test procedures in other regions are also being drafted and brewed. It is an inevitable trend for AC withstand voltage test to replace traditional DC withstand voltage test. 

Variable frequency series resonance test equipment is widely used in power, metallurgy, petroleum, chemical and other industries, and is suitable for the handover and preventive testing of large-capacity, high-voltage capacitive test products.

Variable frequency series resonance withstand voltage test device, complete set of equipment to be shipped

Main uses of variable frequency series resonance withstand voltage device:

1. AC withstand voltage test of 6kV-500kV high-voltage cross-linked cables

2. Power frequency withstand voltage test of 6kV-500kV transformers

3. AC withstand voltage test of GIS and SF6 switches

4. AC withstand voltage test of generators

5. AC withstand voltage test of other high-voltage power equipment such as busbars, bushings, and transformers.

Compared with the original equipment:

Under power frequency conditions, due to the large capacitance of the test product or the high test voltage requirements, the power supply capacity of the test device is also correspondingly required to be high. Traditional power frequency withstand voltage devices (AC withstand voltage test transformers) are often large in size and heavy in weight, which is not convenient for on-site transportation, and is not convenient for arbitrary combination, and has poor flexibility. In comparison, the variable frequency series resonance test device (the volume and weight are about 1/3 to 1/4 of the traditional oil-type test transformer) consists of a variable frequency power supply, an excitation transformer, a reactor, and a voltage divider. Features: small size, light weight, complex structure, high cost, and numerous wiring. The portable AC power frequency withstand voltage instrument (consisting of a dry-type test transformer and a control box) is small in size, light in weight, simple in structure, and highly reliable; it can be easily used on site.

The main products of Shanghai Demiks Power Technology Co., Ltd. include: "Series resonance test equipment, partial discharge test system, high voltage insulation withstand voltage, transformer test, circuit breaker test, relay protection, secondary circuit test, cable line test, lightning arrester insulator tester, SF6 test, oil test, DC system battery test, reactive power compensation generator detection, ground insulation resistance test, power metering test, etc." More than 200 products in 20 categories".

Choose Demiks for electic power safety! Contact email contact@demikspower.com

The partial discharge test system is a system specifically used to measure the partial discharge phenomenon of electrical equipment. It is widely used in transformers, motors, mutual inductors, cables, GIS, switches, lightning arresters and other equipment. The system can monitor and warn the partial discharge phenomenon of the equipment in real time to ensure the normal operation and safety of the equipment.

Definition and purpose of partial discharge test system

The partial discharge test system is to evaluate the insulation status and potential faults of the equipment by monitoring the partial discharge phenomenon in electrical equipment. Partial discharge refers to the discharge phenomenon between the partially bridged conductors of the insulating material in the electrical equipment under the action of the electric field, which may be caused by the concentration of electrical stress inside or on the surface of the insulation layer.

Composition and working principle of partial discharge test system

The partial discharge test system usually consists of the following parts:

‌Partial discharge sensor‌: senses the partial discharge phenomenon in the equipment and converts it into electrical signals.

‌Partial discharge monitoring host‌: receives the signal from the sensor, processes and analyzes the signal.

‌Monitoring platform‌: includes industrial control computers and application software for data storage, analysis and warning.

‌Internet of Things technology‌: such as Alibaba Cloud, used for remote transmission and monitoring of data.

‌Terminal equipment‌: such as computers, mobile phones, tablets, etc., for real-time monitoring and early warning‌

Application scenarios and importance of partial discharge test systems

Partial discharge test systems play an important role in power systems and can be applied to the following scenarios:

‌Online monitoring and real-time early warning of equipment such as switch cabinets, GIS, circuit breakers, substations, transformers, etc.

Help to detect insulation defects of equipment in a timely manner and prevent equipment failures and accidents.

Improve equipment reliability and service life, reduce maintenance costs and downtime.

The main products of Shanghai Demiks Power Technology Co., Ltd. include: "Series resonance test equipment, partial discharge test system, high voltage insulation withstand voltage, transformer test, circuit breaker test, relay protection, secondary circuit test, cable line test, lightning arrester insulator tester, SF6 test, oil test, DC system battery test, reactive power compensation generator detection, ground insulation resistance test, power metering test, etc." More than 200 products in 20 categories".

Choose Demiks for electic power safety! Contact email contact@demikspower.com

What is a frequency series resonance test device?

A frequency series resonance test device is a series resonance test device that uses a tuned inductor and a load capacitor to generate a power frequency series resonance to obtain a power frequency test voltage. The series resonance is composed of an isolation transformer, a frequency modulation and voltage modulation power supply, an excitation transformer, a reactor, and a capacitive voltage divider. The capacitor and the reactor of the test object form a series resonance connection mode; the voltage divider is connected in parallel to the test object to measure the resonant voltage on the test object and to provide an overvoltage protection signal; the frequency modulation power output is coupled to the series resonance circuit through the excitation transformer to provide the excitation power of the series resonance.

The frequency conversion series resonance test device is different from general test instruments. The biggest feature is that the same set of equipment can be used for AC withstand voltage tests of different electrical equipment such as cross-linked cables, transformers, GIS, motors and generators. In addition to the series of typical and commonly used models given in this selection catalog for users to choose, it is usually necessary to design a configuration plan according to the user's test product range and test requirements to meet the test requirements of different regions, different users, and different test products.

The series resonance test device is the latest generation of equipment specially used for AC withstand voltage test of capacitive test products. It is widely used in AC withstand voltage test of various high-voltage cross-linked cables, transformers, generators, GIS switches, and motors. It is a complete set of instruments and equipment for SF6 switch variable frequency series resonance and series harmonic power frequency AC withstand voltage test.

Series resonance is mainly used for:

1. AC withstand voltage test of 6kV-500kV high-voltage cross-linked cable

2. AC withstand voltage test of generator

3. AC withstand voltage test of GIS and SF6 switch

4. Power frequency withstand voltage test of 6kV-500kV transformer

5. AC withstand voltage test of other power high-voltage equipment such as busbar, bushing, and transformer.

Product aliases of series resonance

Variable frequency series resonance AC withstand voltage test device, variable frequency resonance, variable frequency series resonance, series resonance, frequency modulation series resonance, DAXZ series resonance withstand voltage test device, series resonance test equipment, cable withstand voltage test device, power frequency withstand voltage test device, high-voltage cross-linked cable AC withstand voltage test equipment, AC withstand voltage test device, frequency modulation resonance, portable cable AC withstand voltage test device, generator AC withstand voltage test device, GIS AC withstand voltage test equipment, etc.

Components of series resonance

Components of series resonance test device: It consists of variable frequency power supply, excitation transformer, high-voltage reactor and capacitor voltage divider.

The main products of Shanghai DEMIKS Power Technology Co., Ltd. include: "Series resonance test equipment, partial discharge test system, high voltage insulation withstand voltage, transformer test, circuit breaker test, relay protection, secondary circuit test, cableline test, lightning arrester Insulator tester, SF6 test, oil test, DC system battery test, reactive power compensation  Generator detection, grounding Insulation resistance test, power metering test, etc." More than 200 products in 20 categories".

Choose DEMIKS for power safety! Contact email contact@demikspower.com