Transformer main parameters

The main technical data are generally marked on the nameplate of the transformer.

Mainly include: rated capacity, rated voltage and its tap, rated frequency, winding coupling group and rated performance data (impedance voltage, no-load current, no-load loss and total weight of load loss.

A, rated capacity (kVA): rated voltage. Rated current under continuous operation, the capacity can be delivered.

B, rated voltage (kV): the working voltage that the transformer can withstand when operating for a long time. In order to adapt to the needs of changes in grid voltage, transformer high-voltage side are tapped, by adjusting the number of turns of high-voltage winding to adjust the output voltage of the low-voltage side.

C, rated current (A): the transformer in the rated capacity, allowing long-term current through.

D. No-load loss (kW): When the rated voltage at the rated frequency is applied to the terminals of one winding, the active power drawn by the rest of the winding is open circuit. With the core silicon steel sheet performance and manufacturing process, and the applied voltage related.

E, no-load current (%): When the transformer is no-load on the second side at rated voltage, the current passed in the primary winding. Generally expressed as a percentage of the rated current.

F, load loss (kW): the transformer’s secondary winding short-circuit, in the primary winding rated tap position into the rated current, when the transformer power consumption.

G, impedance voltage (%): the transformer’s secondary winding short-circuit, in the primary winding slowly raise the voltage, when the secondary winding short-circuit current is equal to the rated value, when the voltage applied to the primary side. Generally expressed as a percentage of the rated voltage.

H, the number of phases and frequency: the beginning of the three-phase to S, single-phase beginning to D said. China’s national standard frequency f for 50Hz. 60Hz foreign countries (such as the United States).

I, temperature rise and cooling: transformer winding or upper oil temperature and transformer temperature difference between the surrounding environment, known as the winding or upper oil temperature rise. Oil-immersed transformer winding temperature rise limit of 65K, oil surface temperature rise of 55K. cooling methods are also various: oil-immersed self-cooling, forced air cooling, water cooling, tube, sheet type, etc..

J. Insulation level: There are insulation level standards. The insulation level is expressed as follows: the insulation level of transformer with high voltage rated voltage of 35kV and low voltage rated voltage of 10kV is LI200AC85/LI75AC35, where LI200 means that the transformer has high voltage lightning surge withstand voltage of 200kV and frequency withstand voltage of 85kV, low voltage lightning surge withstand voltage of 75kV and frequency withstand voltage of 35kV. withstand voltage of 35kV.

Use of high and low voltage switchgear need to understand the knowledge

Before we use the high-voltage switchgear, we need to understand the structure of the product, such as circuit breakers, contactors, intermediate relays, thermal relays, buttons, indicators, universal transfer switches and travel switches can be said to be the more common components of high-voltage switchgear, the next to introduce you to the following principles and applications of these common electrical components, to understand their role in the electrical circuit to master the usual operating conditions of the components.

(1) circuit breaker

Low-voltage circuit breakers, also known as automatic air switches, can be manually switched, and can be used to distribute electrical energy, infrequent start asynchronous motors, power lines, motors and other protection, when they are seriously overloaded, short-circuit or undervoltage and other faults can automatically cut off the circuit.

Circuit breaker

(2) Contactor

The contactor is composed of two parts: electromagnetic mechanism and contact system. The electromagnetic mechanism is composed of coil, moving iron core and static iron core; the contactor contact system is composed of two parts: main contact and auxiliary contact; the main contact is used to open and close the main circuit, and the auxiliary contact is used to control the circuit.


(3) Thermal Relay

A thermal relay is a relay that operates in reverse time by using the principle of thermal effect generated by the current passing through the component.

Thermal relay

(4) Intermediate Relay

The principle of intermediate relay is to turn an input signal into multiple output signals or amplify the signal relay. In essence, it is a voltage relay, but it has more contacts and sensitive action. When the number of contact pairs of other appliances is not enough, they can be extended with the help of intermediate relays, and there is also the expansion of contact energizing capacity through intermediate relays.

Intermediate relay

(5) Indicator light

The function of the indicator light is to indicate the operation or stopping status of the equipment, to monitor whether the power supply of the control appliance is normal, to use the red light to monitor whether the tripping circuit is normal, and to use the green light to monitor whether the closing circuit is normal.

Indicator light

(6) Transfer switch

The universal change-over switch consists of an operating mechanism, a panel, a handle and several contact holders and other components. The on/off status of each contact is indicated by a black dot when the handle is turned to different gears. A black dot indicates that the contact is closed, while one without a black dot indicates that the contact is broken.

Changeover switch

(7) Schematic diagram of the control mode in the motor contactor.

Low-voltage electrical switch use precautions, the safe use and use of low-voltage electrical switches

Low-voltage electrical switch use precautions, the safe use of low-voltage electrical switch and the use of

The safe use of low-voltage switch

1. Safety precautions for the installation and use of knife switches are as follows.

1) The knife switch should be installed vertically on the switch plate and make the static contacts above. When wiring, the static contact should be connected to the power supply, and the dynamic contact should be connected to the load.

2) When closing the knife switch, it should ensure that the three phases are closed at the same time and the contact is good; when dividing the switch, it should disconnect the three phases at the same time, and ensure that the disconnection is a certain insulation distance.

(3) The knife switch without interrupting cover is generally not allowed to break and close the power load, so as not to burn the knife switch.

1) The knife switch with porcelain bottom and rubber cover should be installed vertically and the handle should be closed upward, not installed upside down and flush.

2) When wiring, the power supply should be connected to the incoming terminal block above the switch, and the load should be connected to the outgoing block below. After such a gate is pulled, no electric shock accident will occur when the fuse is replaced. When wiring, the screws should be tightened and contact resistance should be minimized to avoid overheating.

3) The installation should make close contact between the blade and the clamp seat, and the clamp seat has enough pressure. The blade and clamping seat should not be distorted.

4) Replacement of the fuse must be done with the gate pulled open. The replacement fuse should be the same as the original fuse specification.

3. Precautions for the installation and use of the enclosed load switch are as follows.

1) Enclosed load switch should be installed vertically. The general installation height is 1.3~1.5m from the ground.

2) Enclosed load switch enclosure should be reliably grounded or zeroed.

3) Enclosed load switch inlet and outlet holes should have insulating washers.

4. The following precautions should be taken for the installation and use of the transfer switch.

1) When installing the transfer switch, the handle should be kept in a horizontal rotating position.

2) Since the change-over switch has low breaking capacity, it cannot be used to break the fault current. When used for motor forward and reverse control, the power supply must be turned on only after the motor has completely stopped rotating.

3) When the power factor of the load is low, the contact capacity of the transfer switch should be reduced.

Comprehensive application of intelligent low-voltage switchgear

Low-voltage electrical appliances, its full name is low-voltage switchgear, and its essence belongs to the switch-type components.

We have seen the power grid which is closely related to our life, it consists of power plants, step-up substations, towers and overhead lines for transmitting electricity, step-down substations, main transformers and medium voltage switchgear, main transformers for medium voltage to low voltage, low voltage switchgear, etc., while our electric loads are located at the very end.

Let’s look at the circuit diagram in Figure 1: the leftmost part of the circuit diagram is a 10kV/400V transformer with an angle connection on the MV side and a star connection on the LV side. The low-voltage side has the main incoming switch K1, the system bus, and feeder switches K2 to K5, as well as the power-using load.

The power-using loads in the diagram are represented by R1 to R18. Don’t think they are resistors, they can be microwave ovens, refrigerators, or motors and lighting circuits.

Note: We see that the low voltage side of the transformer is fed at one point, but after distributing the power through the system bus, and then through each feeder switch, the power is distributed to multiple points.

This is called the point-to-multipoint structure of power distribution.
From this we know that the task of the system bus in the original distribution cabinet is to distribute electrical energy, the task of the main incoming switch is to control the total incoming end of electrical energy and line protection, while the task of the feeder switch is to control the feeder circuit and line protection.

Knowing the tasks of the switchgear, what necessary functions should the switchgear have?

These functions include

1. the ability to carry operating currents at rated voltages

2. the ability to carry overload currents and, for a certain period of time, the impact of short-circuit currents

3. to cut off the fault current, to achieve line protection.

These three functions involve theoretical knowledge and technical knowledge is extremely rich. Once you understand these three functions and the corresponding technical parameters of low-voltage electrical appliances, you will also understand the application overview and configuration points of low-voltage switchgear.