Why do we need industrial switches with improved EMC?
What causes packets to be lost on the LAN? There are different options: the backup is configured incorrectly, the network cannot cope with the load or the LAN “storms”. But the reason is not always in the network layer.
The company “N” has made the automated process control system and the video surveillance system of the mine “We will not name names” mine based on the Phoenix Contact switchboards .
There were problems on one part of the network. Between the FL SWITCH 3012E-2FX - 2891120 and FL SWITCH 3006T-2FX - 2891036 switches, the communication channel was extremely unstable.
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The devices were connected by a copper cable laid in one channel with a 6 kV power cable. The power cable creates a powerful electromagnetic field that caused the interference. Ordinary industrial switches do not have sufficient noise immunity, so part of the data was lost.
When FL SWITCH 3012E-2FX - 2891120 switches were installed at both ends, the connection stabilized. These switches comply with IEC 61850-3. Among other things, part 3 of this standard describes the requirements for electromagnetic compatibility (EMC) of devices that are installed in power plants and substations.
Why have improved EMC switches performed better?
It turns out that the stability of data transmission in LAN is influenced not only by the correctness of the equipment setup and the amount of data transmitted. Electromagnetic interference can be the cause of missing packets or a disabled switch: a walkie-talkie that was used near the network equipment, a power cable laid alongside, or a power switch that opened the circuit during a short circuit.
The radio, cable and switch are sources of electromagnetic interference. Switches with improved electromagnetic compatibility are designed for normal operation when exposed to these interferences.
Electromagnetic interference can be of two types: inductive and conductive.
Inductive interference is transmitted through the electromagnetic field "through the air." Also, this interference is called radiated or radiated.
Conductive interference is transmitted through conductors: wires, earth, etc.
Inductive interference occurs when exposed to a powerful electromagnetic or magnetic field. The cause of conducted noise can be switching current circuits, lightning strikes, pulses, etc.
Switches, like all equipment, can be affected by both inductive and conducted interference.
Let's look at the different sources of interference at an industrial facility, and what kind of interference they create.
Radio devices (radios, mobile phones, welding equipment, inductive furnaces, etc.)
Any device emits an electromagnetic field. This electromagnetic field acts on equipment both inductively and conductively.
If the field is generated sufficiently strong, then it can create a current in the conductor that disrupts the signal transmission process. Very powerful interference can lead to equipment shutdown. Thus, inductive effect is manifested.
The operating personnel and security services use mobile phones, walkie-talkies to communicate with each other. Fixed radio and television transmitters are working at the facilities, Bluetooth and WiFi devices are installed on mobile installations.
All these devices are powerful electromagnetic field generators. Therefore, for normal operation in industrial environments, switches need to be able to transfer electromagnetic interference.
Electromagnetic environment is determined by the intensity of the electromagnetic field.
When testing a switch for resistance to inductive effects of electromagnetic fields, a switch with a field strength of 10 V / m is induced on the switch. In this case, the switch must fully function.
Any conductors inside the switch, as well as all cables, are passive receiving antennas. Radio-emitting devices can create conductive electromagnetic interference in the frequency range from 150 Hz to 80 MHz. The electromagnetic field induces a voltage in these conductors. These voltages in turn cause currents that interfere with the switch.
To test the switch for resistance to conductive electromagnetic interference, data ports and power ports are energized. GOST R 51317.4.6-99 establishes a voltage of 10 V for a high level of electromagnetic radiation. In this case, the switch must fully function.
The current in power cables, power lines, ground circuits creates a magnetic field of industrial frequency (50 Hz). The influence of a magnetic field creates a current in a closed conductor, which is a hindrance.
The magnetic field of industrial frequency is divided into:
When the switches are tested for the stability of a magnetic field of industrial frequency, a field with a strength of 100 A / m for a long period and 1000 A / m for a period of 3 s is applied to it. When checking the switches must fully function.
For comparison, a conventional household microwave oven creates a magnetic field strength of up to 10 A / m.
Lightning strikes also interfere with network equipment. They do not last long, but their value can reach several thousand volts. Such interference is called impulse.
Impulse noise can be applied to both the power ports of the switch and the data ports. Due to the high values ​​of overvoltage, they can both disrupt the functioning of the equipment and completely burn it.
A lightning strike is a special case of impulse noise. It can be attributed to microsecond impulse noise high energy.
A lightning strike can be of different types: a lightning strike to an external voltage circuit, an indirect strike, a blow to the ground.
When lightning strikes an external voltage circuit, interference occurs due to the flow of a large discharge current through the external circuit and the ground circuit.
An indirect lightning strike is the discharge of lightning between clouds. During such impacts, electromagnetic fields are generated. They induce voltages or currents in the conductors of the electrical system. This causes interference.
When lightning strikes the ground current flows on the ground. It can create a potential difference in the grounding system of the vehicle.
Exactly the same interference creates switching capacitor banks. Such switching is a switching transient. All switching transients cause microsecond pulsed interference of high energy.
Rapid changes in voltage or current when protective devices are triggered can also lead to the formation of microsecond impulse noise in internal circuits.
To test the switch for resistance to impulse noise, special test pulse generators are used. For example, UCS 500N5. This generator delivers pulses that are different in parameters to the switch ports under test. Pulse parameters depend on tests performed. They can vary in pulse shape, output resistance, voltage, exposure time.
During tests for resistance to the effects of microsecond impulse noise on the power ports are pulses of 2 kV. At the data ports - 4 kV. In this test, it is assumed that the operation may be interrupted, but after the disappearance of the interference, it is independently restored.
Various switching processes may occur in the electrical system: interruptions of inductive loads, opening of relay contacts, etc.
Such switching processes also create impulse noise. Their duration is from one nanosecond to one microsecond. Such pulse interference is called nanosecond pulse interference.
For testing, switches are fed by batches of nanosecond duration. Pulses are fed to the power ports and data ports.
Pulses with a voltage of 2 kV are supplied to the power ports, and 4 kV to the data ports.
During tests on the effects of nanosecond impulse noise switches should be fully functional.
When installing the switch near power distribution systems or power electronic equipment, asymmetrical voltages may be induced in them. Such pickups are called conducted electromagnetic interference.
The main sources of conducted interference are:
Depending on the source of interference is divided into two types:
To test the switches, the power supply and data transmission ports supply the effective voltage of 30V permanently and the effective voltage of 300 V for 1 s. These voltage values ​​correspond to the highest degree of rigidity of the GOST tests.
Equipment must withstand such effects if it is installed in a tough electromagnetic environment. It is characterized by:
Similar conditions can be found at stations or substations.
After straightening, the output voltage always pulsates. That is, the voltage values ​​change randomly or periodically.
If the switches are powered by DC voltage, large voltage ripples can disrupt device operation.
As a rule, all modern systems use special smoothing filters and the ripple level is not great. But the situation changes when installing batteries in the power supply system. When charging batteries, the ripple value increases.
Therefore, it is also necessary to consider the possibility of such interference.
Switches with improved electromagnetic compatibility allow data to be transmitted in a tough electromagnetic environment. In the example with the mine at the beginning of the article, the data cable was exposed to a powerful magnetic field of industrial frequency and conducted interference in the frequency band from 0 to 150 kHz. Ordinary industrial switches could not cope with data transmission in such conditions and packets were lost.
Switches with improved electromagnetic compatibility can fully function when exposed to the following interference:
The company “N” has made the automated process control system and the video surveillance system of the mine “We will not name names” mine based on the Phoenix Contact switchboards .
There were problems on one part of the network. Between the FL SWITCH 3012E-2FX - 2891120 and FL SWITCH 3006T-2FX - 2891036 switches, the communication channel was extremely unstable.
')
The devices were connected by a copper cable laid in one channel with a 6 kV power cable. The power cable creates a powerful electromagnetic field that caused the interference. Ordinary industrial switches do not have sufficient noise immunity, so part of the data was lost.
When FL SWITCH 3012E-2FX - 2891120 switches were installed at both ends, the connection stabilized. These switches comply with IEC 61850-3. Among other things, part 3 of this standard describes the requirements for electromagnetic compatibility (EMC) of devices that are installed in power plants and substations.
Why have improved EMC switches performed better?
EMC - General Terms
It turns out that the stability of data transmission in LAN is influenced not only by the correctness of the equipment setup and the amount of data transmitted. Electromagnetic interference can be the cause of missing packets or a disabled switch: a walkie-talkie that was used near the network equipment, a power cable laid alongside, or a power switch that opened the circuit during a short circuit.
The radio, cable and switch are sources of electromagnetic interference. Switches with improved electromagnetic compatibility are designed for normal operation when exposed to these interferences.
Electromagnetic interference can be of two types: inductive and conductive.
Inductive interference is transmitted through the electromagnetic field "through the air." Also, this interference is called radiated or radiated.
Conductive interference is transmitted through conductors: wires, earth, etc.
Inductive interference occurs when exposed to a powerful electromagnetic or magnetic field. The cause of conducted noise can be switching current circuits, lightning strikes, pulses, etc.
Switches, like all equipment, can be affected by both inductive and conducted interference.
Let's look at the different sources of interference at an industrial facility, and what kind of interference they create.
Interference sources
Radio devices (radios, mobile phones, welding equipment, inductive furnaces, etc.)
Any device emits an electromagnetic field. This electromagnetic field acts on equipment both inductively and conductively.
If the field is generated sufficiently strong, then it can create a current in the conductor that disrupts the signal transmission process. Very powerful interference can lead to equipment shutdown. Thus, inductive effect is manifested.
The operating personnel and security services use mobile phones, walkie-talkies to communicate with each other. Fixed radio and television transmitters are working at the facilities, Bluetooth and WiFi devices are installed on mobile installations.
All these devices are powerful electromagnetic field generators. Therefore, for normal operation in industrial environments, switches need to be able to transfer electromagnetic interference.
Electromagnetic environment is determined by the intensity of the electromagnetic field.
When testing a switch for resistance to inductive effects of electromagnetic fields, a switch with a field strength of 10 V / m is induced on the switch. In this case, the switch must fully function.
Any conductors inside the switch, as well as all cables, are passive receiving antennas. Radio-emitting devices can create conductive electromagnetic interference in the frequency range from 150 Hz to 80 MHz. The electromagnetic field induces a voltage in these conductors. These voltages in turn cause currents that interfere with the switch.
To test the switch for resistance to conductive electromagnetic interference, data ports and power ports are energized. GOST R 51317.4.6-99 establishes a voltage of 10 V for a high level of electromagnetic radiation. In this case, the switch must fully function.
Current in power cables, power lines, ground circuits
The current in power cables, power lines, ground circuits creates a magnetic field of industrial frequency (50 Hz). The influence of a magnetic field creates a current in a closed conductor, which is a hindrance.
The magnetic field of industrial frequency is divided into:
- magnetic field of constant and relatively low intensity caused by currents under normal operating conditions;
- Magnetic field of relatively high intensity, caused by currents under emergency conditions, acting for a short time until the devices trigger.
When the switches are tested for the stability of a magnetic field of industrial frequency, a field with a strength of 100 A / m for a long period and 1000 A / m for a period of 3 s is applied to it. When checking the switches must fully function.
For comparison, a conventional household microwave oven creates a magnetic field strength of up to 10 A / m.
Lightning strikes, emergency conditions in electrical networks
Lightning strikes also interfere with network equipment. They do not last long, but their value can reach several thousand volts. Such interference is called impulse.
Impulse noise can be applied to both the power ports of the switch and the data ports. Due to the high values ​​of overvoltage, they can both disrupt the functioning of the equipment and completely burn it.
A lightning strike is a special case of impulse noise. It can be attributed to microsecond impulse noise high energy.
A lightning strike can be of different types: a lightning strike to an external voltage circuit, an indirect strike, a blow to the ground.
When lightning strikes an external voltage circuit, interference occurs due to the flow of a large discharge current through the external circuit and the ground circuit.
An indirect lightning strike is the discharge of lightning between clouds. During such impacts, electromagnetic fields are generated. They induce voltages or currents in the conductors of the electrical system. This causes interference.
When lightning strikes the ground current flows on the ground. It can create a potential difference in the grounding system of the vehicle.
Exactly the same interference creates switching capacitor banks. Such switching is a switching transient. All switching transients cause microsecond pulsed interference of high energy.
Rapid changes in voltage or current when protective devices are triggered can also lead to the formation of microsecond impulse noise in internal circuits.
To test the switch for resistance to impulse noise, special test pulse generators are used. For example, UCS 500N5. This generator delivers pulses that are different in parameters to the switch ports under test. Pulse parameters depend on tests performed. They can vary in pulse shape, output resistance, voltage, exposure time.
During tests for resistance to the effects of microsecond impulse noise on the power ports are pulses of 2 kV. At the data ports - 4 kV. In this test, it is assumed that the operation may be interrupted, but after the disappearance of the interference, it is independently restored.
Switching reactive loads, “bounce” of relay contacts, switching when rectifying alternating current
Various switching processes may occur in the electrical system: interruptions of inductive loads, opening of relay contacts, etc.
Such switching processes also create impulse noise. Their duration is from one nanosecond to one microsecond. Such pulse interference is called nanosecond pulse interference.
For testing, switches are fed by batches of nanosecond duration. Pulses are fed to the power ports and data ports.
Pulses with a voltage of 2 kV are supplied to the power ports, and 4 kV to the data ports.
During tests on the effects of nanosecond impulse noise switches should be fully functional.
Leads from industrial electronic equipment, filters and cables
When installing the switch near power distribution systems or power electronic equipment, asymmetrical voltages may be induced in them. Such pickups are called conducted electromagnetic interference.
The main sources of conducted interference are:
- power distribution systems, including DC and 50 Hz;
- power electronic equipment.
Depending on the source of interference is divided into two types:
- DC voltage and voltage frequency of 50 Hz. Short circuits and other interruptions in distribution systems generate interference at the fundamental frequency;
- voltage in the frequency band from 15 Hz to 150 kHz. Such interference is usually generated by power electronic installations.
To test the switches, the power supply and data transmission ports supply the effective voltage of 30V permanently and the effective voltage of 300 V for 1 s. These voltage values ​​correspond to the highest degree of rigidity of the GOST tests.
Equipment must withstand such effects if it is installed in a tough electromagnetic environment. It is characterized by:
- the devices under test will be connected to low voltage electrical networks and medium voltage lines;
- devices will be connected to the grounding system of high-voltage equipment;
- power converters are used that inject significant currents into the ground system.
Similar conditions can be found at stations or substations.
AC voltage rectification when charging batteries
After straightening, the output voltage always pulsates. That is, the voltage values ​​change randomly or periodically.
If the switches are powered by DC voltage, large voltage ripples can disrupt device operation.
As a rule, all modern systems use special smoothing filters and the ripple level is not great. But the situation changes when installing batteries in the power supply system. When charging batteries, the ripple value increases.
Therefore, it is also necessary to consider the possibility of such interference.
Conclusion
Switches with improved electromagnetic compatibility allow data to be transmitted in a tough electromagnetic environment. In the example with the mine at the beginning of the article, the data cable was exposed to a powerful magnetic field of industrial frequency and conducted interference in the frequency band from 0 to 150 kHz. Ordinary industrial switches could not cope with data transmission in such conditions and packets were lost.
Switches with improved electromagnetic compatibility can fully function when exposed to the following interference:
- radio frequency electromagnetic fields;
- industrial frequency magnetic fields;
- nanosecond pulse interference;
- microsecond high energy impulse noise;
- conducted interference induced by a radiofrequency electromagnetic field;
- conducted interference in the frequency range from 0 to 150 kHz;
- DC power supply ripple.
Source: https://habr.com/ru/post/448534/
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