Secondary circuits - cables and wires forming a system that connects automation, control, alarm, protection devices, measurements. Thus, the secondary system of the power plant is formed.
Kinds
Secondary chains come in several varieties. So, these include voltage and current circuits. They are distinguished by the presence of devices for measuring indicators of current, power, voltage.
There is also an operational variety. It promotes the transfer of current to the main actuators. Secondary circuits of this kind are represented by electromagnets, contactors, circuit breakers, fuses, keys and so on.
The current circuit that comes from the CT for measurements is most often used to power:
- Instruments that show and measure ammeters, wattmeters, varometers and so on.
- Protective relay systems: remote, against short circuits, circuit breakers and others.
- Devices in order to regulate power flows, emergency control automation.
- A number of devices included in the alarm or blocking system.
In addition, the current circuit is used when there is a need to power devices for converting alternating current into direct current, which are used as sources of operating current.
How to build
Installation of secondary circuits is carried out taking into account a number of rules. So, each device can be connected to 1 or more current sources. This is determined taking into account the power consumption, the required accuracy, the length.
When it comes to a multi-winding transformer, the secondary circuit is an independent current source. All secondary devices that attach to the CTs of one phase are connected to the secondary winding in a specific order. Devices and connecting circuits should constitute a closed system. Do not open the secondary circuit of the current transformer if there is current in the primary. Therefore, it never installs circuit breakers, fuses.
Protection
In order to protect personnel when secondary circuit failures occur, for example, when insulation is overlapped between the primary and secondary structures, protective earths are installed. This is done at the points closest to the CT, at the clamps. Isolation of the secondary circuit is also important in the case when several CTs are interconnected, and it is fixed at one point. Grounding is provided with a fuse-arrester, whose voltage rating does not exceed 1000 V.
Be sure to take into account the characteristics of the primary system, in particular, the ability to power both lines of 2 bus systems. For this reason, secondary currents from the CT, which is supplied to the relay and primary connection devices, are added. But at the same time they do not take into account the differential protection of tires and CBD.
If the connections do not currently work, are subject to repair, then the working cover is removed from the test block. This leads to the fact that the secondary circuits of current transformers are closed and grounded. At the same time, the circuits that went to the protective relays are subject to breaking.
About voltage circuits
The voltage circuits that come from voltage transformers are used to power:
- Measuring devices that indicate and record data - voltmeters, frequency meters, wattmeters.
- Energy meters, oscilloscopes, telemetry devices.
- Protective relay systems - remote, directional and others.
- Automated devices, emergency control, power flows, blocking devices.
- The organs that control the presence of tension.
They are also used to power the rectifier devices, which act as sources of constant operating current.
About grounding
Grounding for protection is always inserted into the secondary circuit. This is done by combining the corresponding device with one of the phase wires or the zero point of the secondary system. Grounding is done at a point that is as close as possible to the assemblies of the VT clamps or next to its terminals.
In the wires on the phase that has been grounded, on the secondary circuit, the installation of circuit breakers between it and the earthing point of the circuit breaker is not carried out. The findings of the voltage transformer windings that were grounded do not connect. The cores of the control cables are laid to the destination - for example, to the busbars. Do not connect the conclusions that have been grounded on different voltage transformers.
During use, a voltage transformer may be damaged, the secondary circuits with the protection of which are connected to automation devices, measurements, and so on. In order to avoid cases of damage, reserve.
If there is a circuit including a dual busbar system, VTs mutually reserve each other when one of the transformers is taken out of operation. If there are 2 busbar systems in the circuit, when switching the connection from one system to the second, the voltage circuits automatically switch.
Always exclude the possibility that the grounded circuits of both transformers are connected. This is extremely important. Practice proves that if this happens, the operation of the protective relay system, automatic devices will be seriously disrupted.
It is always necessary to ensure that the detachable contacts are in good condition, as well as the secondary voltage circuits, operating current, which depart from them.
Operational current
At the moment, they often use operating current in electrical installations. When building its circuits, they necessarily protect them from short-circuit currents. For this purpose, a number of individual fuses or switches are used, in which there are additional contacts for signaling, they feed the secondary circuits with the operating current. It is best to use circuit breakers instead of traditional fuses. They cope with this role more effectively, as practice shows.
The operating current is supplied to the relay protection systems and control of the circuit breakers by means of separate circuit breakers. This is never carried out together with the signaling and blocking circuits.
On power lines, voltage transformers from 220 kV, circuit breakers for primary and backup protective systems are fixed.
An DC-DC circuit always has insulation control devices and also helps to provide warning signals when insulation resistance decreases. In DC circuits, insulation resistance is measured at all poles.
In order for the operation of the devices to be reliable, it is necessary to monitor the proper power supply of the circuit with operational current at each connection. It is best to do this using relays that give an alarm when the voltage drops.
About the term
The technical literature often expresses the concept of “secondary power transmission circuits” in different ways. So, he has synonyms. Often the same phenomenon is called secondary switching circuits. However, many experts consider this replacement unsuccessful. The thing is that the secondary switching circuit most likely refers to the processes of switching electrical circuits, because the term "switching" is the name of the action.
It is important to distinguish between themselves and a number of other concepts. Electric energy is transmitted along the primary circuits. Secondary circuits are most often used with operational power sources. Their voltage is 220 V or 110 V, the use of combined power sources is often noted.
The concept of "secondary power transmission circuits" may include several of their varieties:
- with direct current;
- with alternating current;
- in current transformers;
- in voltage transformers.
It includes several tires with different purposes. To distinguish secondary power circuits from their different sections, a number of special notations are used.
They are numbered, given the polarity of the chains. So, the areas of secondary power circuits with positive polarity are indicated by odd numbers. If the polarity is negative, even ones are used.
If we are talking about a secondary electrical circuit with alternating current, then they are denoted by numbers in order, not dividing by the sign of parity. Sometimes, along with numerical designations, letters are also used.
Features
In voltage transformers, which are placed in power plants or substations with a number of switchgears, relay boards and control panels are placed far enough from each other, grounding them in a place remote from the voltage transformer. Due to this feature, it is impossible to install circuit breakers that would protect the transformer in the event of a short circuit.
The secondary circuit, which is powered by a battery, has some nuances. They are always taken into account when choosing fuses.
The term "secondary circuit" refers to wires and cables, including combining equipment designed to measure values in the primary circuit.
They are used in filling and filling cranes that work with liquid metals. Also used in high-speed cranes. In both cases, the circuit is represented by wires with copper conductors, as well as with heat-resistant insulation.
It is important to consider that fuses must be open so that they can be easily inspected and repaired without lowering the voltage across the entire assembly.
The circuit consists of insulated wires bundled into threads. If there are more than 25 pieces in a single stream of wires, then working with them becomes excessively complex.
Each stream is laid along the shortest path, placing it in the horizontal or vertical direction. It is permissible to deviate them from these positions by only 6 mm in each meter of length. Forming flows, wires never cross. Each branch is held at right angles. It is important that their rows are even. Typically, 10-15 wires are taken per thread. In the lower rows are the longest wires, and in the upper ones with the smallest length.
If the secondary circuit in the cabinets and panels includes copper wires, then in the external connections - between the cabinets and panels - control cables. Sometimes the external connection is implemented using wires in steel pipes.
In engines
Often questions regarding the secondary ignition circuit arise for motorists. The ignition system in the car ignites the combustible mixture in the engine at the right time. It helps to change the ignition timing, taking into account the load on the engine.
The coil ignition system consists of a primary and secondary circuit of the ignition coil.
Sometimes the car owner needs to check the ignition coil. It provides the whole system, creating a spark between the candles. Many engines have only one coil, but sometimes there are two.
It is the coil that is the voltage transformer, turning it into thousands of volts. Secondary voltage produces a spark in the gap of the spark plug electrodes. Its indicator is determined by the clearance, electrical resistance of the spark plug, wires, fuel composition, engine load. The maximum voltage rating is 40,000 V, it often changes.
Principle of operation
The coil has 2 windings wound around a metal core. Primary with hundreds of turns and 2 external contacts of the coil are interconnected. A positive terminal is connected to the battery, and a negative one is connected to the ignition module and body weight.
In the secondary circuit there are thousands of turns, it is connected with the positive pole to the primary, and negative - to the output in the center of the coil.
The number of turns in other chains fits into the ratio of 80: 1. With an increase in the proportion, the output voltage of the coil also increases. The highest power coils have the most significant proportion of turns.
When the primary winding is shorted to ground, an electric current is released. So, by means of the appeared magnetic field, the coil is charged.
Next, the ignition modules open the primary circuit. Then the field suddenly disappears. A lot of energy remains in the coil, and it transfers the current to the secondary circuit. Voltage can increase by more than a hundred times. At this moment, a spark “runs through”.
Malfunctions
Ignition coils are reliable, robust devices. But sometimes their malfunctions also occur. So, among the reasons for the appearance of defects are overheating, vibration. This leads to damage to the windings, a violation of insulation, resulting in a short circuit, and the circuit is interrupted. The biggest danger for them is overload, which is caused by damage to candles or high-voltage wires.
In cases where the spark plugs are damaged, too high resistance arises in them. The voltage in the coil can increase up to the formation of breakdowns in the insulation.
Insulation can be damaged due to reaching a voltage of 35,000 V. When this indicator is reached, the voltage decreases, an ignition misfire is formed under loads, the coil will not provide enough voltage for the engine to work.
When a battery is connected to its positive contact, and when a short to ground is not created, a spark is created - this is a sure sign that the coil is completely out of order and must now be replaced.
Diagnostics
When a problem occurs in the ignition system, which is classified as a distribution type, it affects all engine cylinders. Its launch turns into a very difficult task. When the engine is running, but sometimes ignores, and the “Check Engine” lamp lights up, then it is time to use the diagnostic scanner. Use it to check the code that is associated with the misfire.
Nevertheless, such a problem can be associated with malfunctions in the fuel supply, for this reason it is impossible to immediately accurately diagnose a malfunction in the coil, candles or high-voltage wires.
And here it is important to know the primary and secondary circuits. If there is no corresponding count, then the resistance in the circuits is necessarily measured. To do this, use a digital multimeter. It is important to see in what condition the spark plugs are, what is the gap between the contacts. Often a malfunction is indicated by the color of soot on candles. Probably, the pass appeared due to the presence of oil deposits, heavy soot. It is important to inspect the high-voltage wires in order to make sure that the resistance in them is within the established norm.
When it is established that the coil, its circuits are normal, it can be assumed that the fuel nozzle is dirty or damaged. Therefore, be sure to check it out. When the probability of its malfunction is excluded, then the tests are subjected to compression, the valves look to see if there has been a leakage of the cylinder head gasket.
But if the engine is spinning and there is no spark, then probably the fault is in the control circuit. Verification is carried out guided by a number of strict rules.
Warning
Under no circumstances should you disconnect high-voltage wires from spark plugs or coils to check for sparks. The risk of electric shock is extremely high. In addition, there is a chance that secondary voltage will severely damage the device. Therefore, when the need arises in this procedure, testers for candles are used, as well as a probe.
If there is a problem in the coil, then measure the resistance in both windings using an ohmmeter. When deviations from normal values are detected, the coil is replaced. It is also checked using an ohmmeter with 10 MΩ input resistance.
To test it, connect the measurement wires to the contacts in the primary circuit. Most often, the resistance varies between 0.4 - 2 ohms. If a zero level has been detected, then this is a sure sign that a short circuit has occurred in the coil. If the resistance turned out to be high, then the circuit broke.
Secondary resistance is measured between the positive terminals and the high voltage terminals. Modern devices most often have a resistance of 6000-8000 ohms, but sometimes an indicator of 15000 ohms is also found.
In another variation of the coils, the primary contact may be located in the connectors or hidden.
Danger
If you do not apply the acquired knowledge and leave the coil faulty, it will one day damage the entire PCM unit. The thing is that the reduced resistance of the primary circuit leads to an increase in the current in the coil. Therefore, the chances that the PCM block breaks are increasing.
Secondary voltage can also decrease, and sparking can weaken, engine starting will be accompanied by many difficulties, misfires will occur again and again.
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Replacement
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Before starting the installation, the specialist gets acquainted with the installation, and sometimes the circuit diagrams. Then he determines which method will carry out the laying, compose the flow of wires. There are a number of rules in this procedure. So, the wires that belong to 1 mounting unit are connected in one stream.
Also remember that a large number of wires will require more work on them. Never lay the wires in such a way that they cover the contacts of the devices, part of the fasteners.
Laying many layers of streams, in a row do not stack more than 10 wires at once. The wires of one row are connected to adjacent contacts of devices or clamps. The wires that are laid between the connections are always intact. In no case should you engage in their coalescence.
The appearance of each thread will depend on how the wires are prepared. If the amount of work is small, then the preparation of the wire will be to cut it to the desired length and trim.
Laying methods
There are several ways to install a secondary circuit. If custom panels are made, then most often they do this by laying wires directly. For mounting using this method, you will need a panel made in an appropriate way. If it has equipment to connect the wires in front, then at a distance of about 40 mm from the clamps, a series of holes are drilled, the diameter of which is 10.5 mm. A sleeve of type U-457 is inserted into each. Stacked clamps are placed on the front side. The same holes are made in the clamps and bushings are inserted. Wires are laid on the back of the panel. They are brought out by means of plugs to the front side.
Before attaching the wires coming from the sleeve, they are bent into a semicircle, creating a compensator. They are also pulled as tight as possible, which allows you to create a more aesthetic look on the other side of the panel. The longest of them are fastened with mounting tapes. Wires that go in the same direction do not need to be pulled together.
There is another way of fastening - using Loskutov strips. To do this, pre-draw the laying lines. When bonding with a wire is carried out using brackets, holes are also made, threads are cut. For the manufacture of staples take sheet steel, whose thickness is about 0.7 mm Their size will depend on the number of wire flow.
Usually the wires are fastened using strips of sheet steel, which are welded to the panels by spot welding according to the Loskutov method. The distance between them is 150-200 mm.
Some areas of the route are divided into several equal intervals. Welding is carried out at 2 to 4 points. Along the track lay an insulating electrocatronic strip. Also, gaskets for insulation are placed between the wires with strips.
Streams with wires are pulled together by strips that pass through buckles. The ends of each strip are bent, and the excess is trimmed.
Laying wires in streams goes like this:
- Having cut the wires, they are put into the stream, and then connected to the clamps of the devices.
- Be sure to ensure that there are no deviations from horizontal and vertical position.
- If the track is chosen correctly, the lines are straight, then the device has a pleasant appearance.
- The bending of the wires is carried out in such a way as not to damage their insulation. For this reason, the bending radius should be at least 2 outer diameters of the wire. Bending is done manually, never bending the wires again. Spread them tightly.