Measuring transformers. Electrical measuring instruments
The purpose of measuring transformers is to turn on test instruments. These devices are used, as a rule, in an alternating current circuit. With the help of them you can conduct various voltage measurements. in this case, completely isolated, and the current is regulated by a transformer. If we are talking about testing the current, then ammeters are used. At the same time indicators of electrical voltage can be recorded using a voltmeter.
In addition to transformers, ohmmeters are often connected. With the help of them in the circuit it is possible to determine the electrical resistance. Multimeters are combined measuring devices. The frequency of oscillations in the network can be determined using a frequency meter. If the voltage in it is quite high, then one cannot do without a transformer in this situation. Separately, we should also mention the wattmeters and varmeters.They are designed to measure the power of electric current.
Main types of transformers
To date, these main types of measuring transformers are distinguished:
- Voltage devices.
- DC models.
- AC devices.
Additionally, the separation of transformers occurs by the magnitude of the transformation ratio. In this case, single-range and multi-band modifications are distinguished. Depending on the type of installation, the devices are divided into internal and external. Also, the transformer can be embedded. Additionally, there are overhead and even portable modifications. Some still share transformers by type of dielectric. Today it is possible to distinguish oil, dry and gas-filled subspecies.
What does a transformer consist of?
The device of measuring transformers of various types is quite similar, but there are still differences. If we consider the voltage devices, they include the magnetic core and the secondary winding. At the top of the device must be located mounting ring. In turn, the conductor is in the middle of the device.Modifications of direct current involve the use of several magnetic cores and a core. The winding in this case is primary. The conductor in the device passes under the fastening ring.
How is the test?
Tests of measuring transformers are carried out using a megohm meter. In this case, it is necessary to make measurements of the insulation characteristics. Additionally, a voltmeter should be used for this purpose. Connection to the network is carried out through the conductors. The resistance of each phase is checked separately. Additionally, transformers can be tested for electrical loss factor. In this case, the measurement of the tangent of the angle. With the help of an ammeter, it is possible to evaluate the device winding.
AC and DC devices
Measuring transformers of alternating current, as a rule, are produced built-in type. They use only primary winding. They are ideally suited for installation on a support plane. The maximum parameter of the input voltage can be 500 V. Passage modifications are used only as input systems.At the same time, they are not suitable for distribution works.
Additionally, it should be borne in mind that many models are made with sleeves. They are also called tire devices. DC transformers are characterized by the presence of a core. As a rule, it is installed electromagnetic type. These devices work as ordinary amplifiers. In the process of increasing the voltage of the circuit, magnetization of the element occurs. The secondary winding in this situation serves to amplify the current.
Today, voltage measuring transformers are available in various types. The most common subspecies can be considered single-phase modifications. Their capacity is quite high. The process of induction is carried out quickly. Grounding transformers are usually available in three phases. Their threshold voltage parameter reaches 400 V. There are also cascade models. The primary winding of these devices is divided. Each section passes a current through itself separately. Capacitive modifications are distinguished by the presence of a divider. There is one secondary winding.
Single-range voltage measuring transformers are usually manufactured with cores. They are installed in the circuit with alternating current. At the same time, the threshold voltage indicator should not exceed 300 V. If we consider the temperature characteristics, then the devices are able to operate the maximum at 40 degrees.
The operating voltage in the circuit must be maintained at 200 V. The nominal frequency of the device does not exceed 50 Hz on average. In terms of accuracy, the models are quite different. The phase angle error in this case depends on the throughput of the secondary winding. The transformation ratio of the device is on average 50%. Primary current can be perceived by the system up to 3 A.
Transformers of this type are ideally suited for an alternating current circuit. In this case, the maximum voltage is maintained by them at the level of 500 V. The accuracy class of the device depends on the type of core that is installed. With voltmeters, many modifications can work. Separately, it should be noted the high operating frequency range.
If you operate a transformer in a circuit with alternating current, then this indicator is on average at 55 Hz. The phase angle error in this case will be minimal. The threshold voltage parameter of the device basically does not exceed 300 V. Terminals are used to connect measuring instruments. Grounded modifications of this type of transformer are produced quite rarely.
Measuring current transformers with oil dielectrics today are very common. They can be used in the circuit with alternating current. In this case, the threshold voltage parameter should not exceed 300 V. The accuracy class of the device depends solely on the type of core. The minimum frequency of the device is at 3 Hz. At the same time, the maximum measuring current transformers are able to operate at 55 Hz.
The load parameter in the circuit, as a rule, does not exceed 5 A. Pincers for connecting with devices are used. On the reference plane, transformers can be installed. Models with a grounding system are produced quite often.Additionally, today there are tire modifications. They are used, as a rule, as input devices.
Transformers with gas-filled dielectrics
Measuring transformers of this type can boast a high frequency of 60 Hz. In this case, at least the devices are operated at 5 Hz. In order to connect the device, you need a circuit with a constant current. Loads these devices are able to withstand a maximum of 6 A. Use the model at temperatures above 45 degrees is prohibited. With all current-measuring devices this device is able to interact.
Limiting the threshold voltage in the system is due to the core. In this case, the magnetic circuits in the device, as a rule, there are two. Contacts in this case are used with a protective tire. In this case, the sleeve modifications are quite rare. Separately, it should also be mentioned that there are many grounded transformers. They use only primary winding. At the same time its division into sections does not occur.
Dry dielectric devices
Measuring transformers with dry dielectrics most often work on a pair with multimeters. At the same time, voltmeters and ammeters can also be connected to them. Due to the high threshold voltage, the accuracy of the results will be high. Wattmeters are connected to models of this type quite rarely.
This is due to a greater extent with a high resistance indicator inside the circuit. Additionally, it should be noted that today there are many built-in modifications. In this case, the threshold voltage parameter does not exceed 330 V. Their bushings are rarely used. In this case, the connectors for the models are various.
Connect the transformer to the circuit with alternating current possible. The maximum load on the system can be around 5 A. In order for the core to work properly, you should monitor the operating voltage parameter. Magnetic in the device, as a rule, there are two. Pass-through modifications of transformers are rarely available.