Arc protection system with the ability to operate on a current signal
In the classical sense, arc protection in Russia is a quick protection against short circuits, based on the registration of the light spectrum of an open electric arc in the switchgear, the most common method of recording the spectrum of light by means of fiber-optic sensors is used mainly in the industrial sector, but with the advent of new products in the field of arc protection in the residential sector, namely modular AFDDs operating on a current signal, allowing the installation of arc protection on outgoing lines, including distribution to Boxes, cables, connections, sockets, etc., interest in this topic is growing.
However, manufacturers do not really spread about the detailed and detailed arrangement of modular products (if someone has such information, I will only be glad to have links to the sources of such information), another thing is an arc protection system for the industrial sector, with a detailed user manual of 122 pages , where the principle of action is described in detail.
Consider, for example, the VAMP 321 arc protection system from Schneider Electric, which includes all arc protection functions, such as current overload and arc monitoring.
- Current control in three phases.
- Zero sequence current.
- Event Logs, Alarm Recording.
- The operation is either simultaneous in current and light, or only in light, or only in current.
- The response time of the output with a mechanical relay is less than 7 ms, with the optional IGBT card, the response time is reduced to 1 ms.
- Customizable response zones.
- Continuous self-control system.
- The device can be used in various systems of arc protection of distribution networks of low and medium voltage.
- The arc flash detection system and arc protection measures the short circuit current and the signal through the channels of the arc sensor and, in the event of a short circuit, minimizes the burning time by quickly shutting off the supply of current supplying the arc.
Matrix correlation principle
When setting the activation conditions for a specific stage of arc protection, logical summation is applied to the outputs of the light and current matrices.
If the protection level is selected in only one matrix, it works either by the current condition or by the light, so you can configure the system to work only by the current signal.
Signals available for monitoring when programming protection stages:
- Currents in phases.
- Zero sequence current.
- Linear voltages.
- Phase voltages.
- Voltage zero sequence.
- The sum of the phase currents.
- Direct sequence current.
- Negative sequence current.
- The relative value of the negative sequence current.
- The ratio of the currents of the reverse and zero sequences.
- Direct sequence voltage.
- Negative sequence voltage.
- Relative value of negative sequence voltage.
- The average current value in the phases (IL1 + IL2 + IL3) / 3.
- Average voltage value UL1, UL2, UL3.
- The average voltage value is U12, U23, U32.
- Distortion factor IL1.
- Distortion factor IL2.
- Distortion factor IL3.
- The coefficient of nonlinear distortion Ua.
- RMS value of IL1.
- RMS value of IL2.
- RMS value of IL3.
- The minimum value of IL1, IL2, IL3.
- The maximum value of IL1, IL2, IL3.
- The minimum value is U12, U23, U32.
- The maximum value is U12, U23, U32.
- The minimum value is UL1, UL2, UL3.
- The maximum value is UL1, UL2, UL3.
- The background value of Uo.
- The rms value of Io.
Alarm recording can be used to save all measurement signals (currents, voltages, information on the status of digital inputs and outputs). Digital inputs also include arc protection signals.
Recording can be started by triggering or triggering any protection level or by any digital input. The trigger signal is selected in the matrix of output signals (vertical signal DR). Also, recording can be started manually.
Non-volatile memory of the device is implemented using a large capacity capacitor and low-power RAM.
When the auxiliary power is turned on, the capacitor and RAM are powered by an internal source. When the power source is turned off, the RAM begins to receive power from the capacitor. It will store information as long as the capacitor is able to maintain acceptable voltage. For a room with a temperature of + 25 ° C, the operating time will be 7 days (high humidity reduces this parameter).
Non-volatile random access memory is used to store emergency records and an event log.
The functions of the microcontroller and the integrity of the wires connected with it along with the serviceability of the software are controlled by a separate self-monitoring network. In addition to control, this network tries to restart the microcontroller in case of a malfunction. If the reboot is unsuccessful, the self-monitoring device sends a signal to start the indication of permanent internal damage.
In the event that the self-monitoring device detects permanent damage, it blocks other output relays (except for the output relay of the self-monitoring function and the output relays used by the arc protection).
The internal power supply is also controlled. In the absence of additional power, an alarm signal is automatically received. This means that the output relay for internal damage is energized if the auxiliary power supply is turned on and no internal damage is detected.
The central unit, input / output devices and sensors are monitored.
Measurements used by the arc protection function
Three-phase current and earth fault current measurements for arc protection are carried out electronically. The electronics compares the current levels with the values of the tripping settings and generates binary signals “I >>” or “Io >>” for the arc protection function in case of exceeding the limit. All current components are taken into account.
The signals “I >>” and “Io >>” are connected to the FPGA chip, which performs the function of arc protection. Measurement accuracy for arc protection is ± 15% at 50Hz.
Harmonics and General Non-sinusoidality (THD)
The device calculates THD as a percentage of currents and voltages at the fundamental frequency.
Harmonics from the 2nd to the 15th are taken into account for phase currents and voltages. (The 17th harmonic will be partially taken into account in the value of the 15th harmonic. This is due to the principles of digital measurement.)
Voltage Measurement Modes
Depending on the type of application and current transformers available, the device can be connected either to a zero sequence voltage, a linear or phase voltage. The adjustable parameter “Voltage measurement mode” must be set in accordance with the connection used.
The device is connected to a zero sequence voltage. Directional earth fault protection available. Line voltage measurement, energy measurement and overvoltage and undervoltage protection are not available.
The device is connected to line voltage. Measurement of voltage in one phase and protection for lowering and increasing voltage are available. Directional ground fault protection is not available.
The device is connected to one phase voltage. Single phase voltage measurements are available. In networks with earthed and compensated neutral, undervoltage and overvoltage protections are available. Directional ground fault protection is not available.
In a three-phase system, voltages and currents can be decomposed into symmetrical components, according to Fortescue.
Symmetrical components are:
- Direct sequence.
- Inverse sequence.
- Zero sequence.
This device allows you to control up to six objects, such as a switch, disconnector or grounding knife. Control can be carried out on the basis of the "choice-action" or "direct control".
The device supports user program logic for logical signal expressions.
Available features are:
- Exclusive OR.
- RS & D flip-flops.