The three-phase five-wire system uses yellow, green, red, and light blue colors to indicate U, V, W, and N protection grounding lines.
When the transformer is in operation, the current of each phase of the transformer should not exceed the rated current; the maximum unbalance current should not exceed 25% of the rated current. After the transformer is put into operation, it should be inspected regularly.
In the system powered by the same transformer, it is not advisable to protect the grounding and protection from zero.
The rated voltage of the secondary winding of the voltage transformer is generally 100V.
The secondary side of the voltage transformer must not be shorted during operation. Because of the large short-circuit current generated during the short circuit, it is possible to burn out the transformer. For this purpose, the primary and secondary sides of the voltage transformer are equipped with fuses for protection.
One end of the secondary side of the voltage transformer must be grounded. This is to prevent the first and second coils from breaking into the secondary side when the secondary coil is insulated, which jeopardizes the safety of the person and equipment.
The secondary side of the current transformer is close to the short circuit condition during operation. The rated current of the secondary coil is generally 5A.
The secondary side of the current transformer must never open the circuit during operation.
One end of the secondary side of the current transformer must be grounded to prevent the primary side from breaking into the secondary side when the primary and secondary coils are insulated.
When the current transformer is connected, attention should be paid to the polarity of the primary and secondary coils. The transformer of our country adopts the labeling method of reducing polarity.
When installing, be sure to pay attention to the wiring is correct and reliable, and the secondary side is not allowed to connect the fuse or switch. Even if the instrument or other device on the secondary side is to be removed for some reason, the secondary side must be short-circuited before being removed.
Low-voltage switch refers to isolation switch, circuit breaker, fuse, etc. below 1KV
The load controlled by the low-voltage power distribution device must be clearly separated, and it is strictly forbidden to control and confuse.
The interlocking device of the low-voltage power distribution device and the self-supplied generator equipment should be reliable. It is forbidden to run the power generation equipment in parallel with the grid.
Insulation mats shall be laid on the channels for operation and maintenance of the low-voltage power distribution equipment, and it is forbidden to stack other items on the passages.
When connecting the device: connect the device first, followed by the power supply.
When disassembling the device: first remove the power supply, then remove the device.
When connecting the line: first connect the zero line, then connect the fire line.
When removing the line: first remove the fire line, then remove the zero line.
Low-voltage fuses cannot be used as overload protection for electric motors.
The rated voltage of the fuse must be greater than or equal to the operating voltage of the distribution line.
The rated current of the fuse must be greater than or equal to the rated current of the melt.
The breaking capacity of the fuse must be greater than the maximum short-circuit current that may occur on the distribution line.
The choice of the rated current of the melt must meet the normal operating current of the line and the starting current of the motor.
For short-circuit protection of loads such as electric furnaces and lighting, the rated current of the melt is equal to or slightly larger than the rated current of the load.
For a single motor, the rated current of the melt is ≥ (1.5-2.5) rated current of the motor
The rated current of the melt is in the power distribution system, and the upper and lower stages should be coordinated to achieve selective protection. The next level should be smaller than the previous level.
Porcelain plug-in fuses should be installed vertically, and qualified fuses must be used. The fuses must not be replaced by other copper wires.
The power supply line of the screw fuse should be connected to the center terminal of the base, and the output line of the load should be connected to the terminal block of the threaded case.
When replacing the melt, the electrical equipment must be disconnected first to prevent arcing.
The fuses should be installed on each phase line. It is forbidden to install fuses on the neutral line of two-phase three-wire or three-phase four-wire loop.
The fuse is mainly used for short circuit protection
When the fuse is used for isolation purposes, the fuse must be installed at the head end of the line.
The function of the fuse is short circuit protection. Isolated power supply, safe maintenance.
The knife switch function is to isolate the power supply and safely repair it.
The rubber cover bottom knife switch is generally used as a control switch for electric lighting circuits and electric heating circuits, and can also be used as a distribution switch for branch circuits.
The three-pole rubber cover knife switch can be used to infrequently start the motor control switch when the capacity is properly reduced.
The input terminal of the three-pole rubber cover knife switch power supply should be placed on the inlet of the static contact end, and the electrical equipment should be connected to the outlet of the fuse below.
When the knife switch is turned off, the handle should be down. When the knife is turned on, the handle should be up, not flipping or flat.
The function of the three-pole rubber cover knife switch is short circuit protection. Isolated power supply, safe maintenance.
The housing of the low voltage load switch should be reliably grounded.
When the automatic air switch is selected as the main switch, there must be obvious breaking points on the incoming line side of these switches, and the disconnecting point, the knife switch or the fuse can be used for the obvious breaking point.
The main function of the fuse is overload or short circuit protection.
Capacitor shunt compensation is to connect the capacitor directly to the same circuit on the compensated device to improve the power factor.
There are several measures to improve the power factor, and the most convenient method is to parallel compensate the capacitor.
The wall switch should be 1.3 meters from the ground and the wall socket should be 0.3 meters.
Pull switch should be 2-3 meters from the ground
The electricity meter should be 1.4-1.8 meters from the ground.
The entrance line should be 2.7 meters from the ground
Roads, first and second grade roads, electric lanes, main rivers, weak lines, special ropeways, etc., should not have joints.
The plastic sheathed wire is mainly used for indoor clearing and laying, and should not be directly buried in the plastering layer for dark laying.
Wire through pipes generally require that the total cross-sectional area of ​​the wires within the pipe (including the insulating layer) be no more than 40% of the cross-sectional area of ​​the inner diameter of the pipe.
There shall be no joints in the pipe, and the joints shall be in the junction box; different power circuits, different voltage circuits, alternate circuits, working lighting and emergency lighting shall not be installed in the same pipe.
When the pipe is a steel pipe (iron pipe), the wires of the same AC circuit must be worn in the same pipe, and one wire is not allowed to pass through a steel pipe.
No more than 8 wires are installed in one tube.
When the pipe is a steel pipe (iron pipe), the pipe must be reliably grounded.
When the pipe is a steel pipe (iron pipe), a plastic protective cover must be added at both ends of the pipe outlet.
A wire-splicing pipe with a length of more than 30 meters (semi-hard pipe) should be installed in the middle.
A wire-splicing pipe with a length of more than 40 meters (iron pipe) should be installed in the middle.
The wire is threaded through the tube and has a curved tube length not exceeding 20 meters. A junction box should be installed in the middle.
The wire is threaded through the tube and has two curved conduits that are no longer than 15 meters in length. A junction box should be installed in the middle.
The wire is piped and has three curved conduits that are no longer than 8 meters in length. A junction box should be installed in the middle.
When using multi-phase power supply, the color selection of the wire insulation of the same building should be the same, that is, the protective wire (PE) should be green/yellow two-color line, the neutral line (N) line should be light blue; the phase line is L1- Yellow, L2-green, L3-red. The single-phase power supply switch line is red, and the switch is usually white or yellow.
The joint position of the wire should not be fixed at the insulator, and the joint position should be more than 0.5 m away from the wire fixing, so as not to interfere with the tie and break.
Capacitor Leakage Test Power Supplies
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