In the classical sense, arc protection in Russia is a high-speed short-circuit protection based on registering the light spectrum of an open electric arc in a switchgear, the most common method of registering the light spectrum using 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 junction boxes, cables, connections, sockets, etc., interest in this topic is increasing.
However, manufacturers do not talk much about the detailed and detailed design of modular products (if someone has such information, I will only be happy to provide links to sources of such information), another thing is the arc protection system for the industrial sector, with a detailed user manual on 122 pages , where the principle of operation is described in more detail.
Consider, for example, the VAMP 321 arc protection system from Schneider Electric, which includes all arc protection functions such as overcurrent and arc detection.
Functional
- Current control in three phases.
- Zero sequence current.
- Event logs, recording emergency modes.
- Operation either simultaneously by current and light, or only by light, or only by current.
- The response time of the output with a mechanical relay is less than 7ms, with the optional IGBT card, the response time is reduced to 1ms.
- Customizable trigger zones.
- Continuous self-monitoring system.
- The device can be used in various arc protection systems for low and medium voltage distribution networks.
- The arc flash detection and arc protection system measures the short circuit current and signal through the arc sensor channels and, in the event of a short circuit, minimizes burning time by quickly turning off the current supplying the arc.
Matrix correlation principle
When setting the conditions for activation of a particular stage of arc protection, logical summation is applied to the outputs of the light and current matrices.
If the protection stage is selected in only one matrix, it works either according to the current condition or according to the light condition, so you can configure the system to work only on the current signal.
Signals available for monitoring when programming the protection stages:
- Currents in phases.
- Zero sequence current.
- Line voltages.
- Phase voltages.
- Zero sequence voltage.
- Frequency.
- Sum of phase currents.
- Positive sequence current.
- Negative sequence current.
- The relative value of the negative sequence current.
- Ratio of negative and zero sequence currents.
- Positive sequence voltage.
- Negative sequence voltage.
- The relative value of the negative sequence voltage.
- Average value of current in phases (IL1+IL2+IL3)/3.
- Average voltage value UL1,UL2,UL3.
- Average voltage U12,U23,U32.
- Nonlinear distortion factor IL1.
- Nonlinear distortion factor IL2.
- Nonlinear distortion factor IL3.
- Nonlinear distortion coefficient Ua.
- RMS value of IL1.
- RMS value of IL2.
- RMS value of IL3.
- Minimum value IL1,IL2,IL3.
- Maximum value IL1,IL2,IL3.
- Minimum value U12,U23,U32.
- Maximum value U12,U23,U32.
- Minimum value UL1,UL2,UL3.
- Maximum value UL1,UL2,UL3.
- Background value Uo.
- RMS value of IΠΎ.
Emergency Recording
Alarm recording can be used to save all measurement signals (currents, voltages, information about the states of digital inputs and outputs). The digital inputs also include arc protection signals.
Start recording
Recording can be triggered by triggering or tripping any protection stage or any digital input. The trigger signal is selected in the output signal matrix (DR vertical signal). Recording can also be started manually.
Self-control
The non-volatile memory of the device is implemented using a high-capacity capacitor and low-power RAM.
When the auxiliary power supply is enabled, the capacitor and RAM are powered internally. When the power supply is turned off, the RAM begins to draw power from the capacitor. It will retain information as long as the capacitor is able to maintain an acceptable voltage. For a room with a temperature of +25C, the operating time will be 7 days (high humidity reduces this parameter).
Non-volatile RAM is used to store records of emergency modes and the event log.
The functions of the microcontroller and the integrity of the wires associated with it, along with the health of the software, are controlled by a separate self-monitoring network. In addition to monitoring, this network tries to reset the microcontroller in case of a malfunction. If the reboot fails, the self-monitoring device signals the start of permanent internal fault indication.
In case the watchdog detects a permanent fault, it blocks the other output relays (except the watchdog output relay and the output relays used by the arc protection).
The internal power supply is also monitored. In the absence of additional power, an alarm is automatically sent. This means that the internal fault output relay is energized if the auxiliary power supply is on and no internal fault is detected.
The central unit, input/output devices and sensors are monitored.
Measurements used by the arc protection function
Measurements of the current in three phases and the earth fault current for arc protection are carried out electronically. The electronics compares the current levels with the pickup setpoints and outputs the binary signals βI>>β or βIo>>β for the arc protection function if the limit is exceeded. All current components are taken into account.
The βI>>β and βIo>>β signals are associated with the FPGA chip, which performs the arc protection function. The measurement accuracy for arc protection is Β± 15% at 50Hz.
Harmonics and total non-sinusoidality (THD)
The device calculates THD as a percentage of currents and voltages at the fundamental frequency.
Harmonics from 2nd to 15th are taken into account for phase currents and voltages. (The 17th harmonic will be partially included in the 15th harmonic value. This is due to the principles of digital measurement.)
Voltage measurement modes
Depending on the type of application and the available current transformers, the device can be connected to either zero-sequence, line-to-line or phase voltage. The configurable parameter βVoltage measurement modeβ must be set according to the connection used.
Available modes:
"U0"
The device is connected to the zero sequence voltage. Directional earth fault protection available. Line voltage measurement, energy measurement and overvoltage and undervoltage protection are not available.
"1LL"
The device is connected to line voltage. Single-phase voltage measurement and undervoltage and overvoltage protection are available. Directional earth fault protection is not available.
β1LNβ
The device is connected to one phase voltage. Voltage measurement in one phase is available. In networks with solidly grounded and compensated neutral, undervoltage and overvoltage protections are available. Directional earth fault protection is not available.
Symmetrical components
In a three-phase system, voltages and currents can be decomposed into symmetrical components, according to Fortescue.
The symmetrical components are:
- direct sequence.
- Reverse sequence.
- Zero sequence.
Controlled objects
This device allows you to control up to six objects, such as a circuit breaker, disconnector or earthing switch. Control can be carried out on the principle of βchoice-actionβ or βdirect controlβ.
Logic functions
The device supports user programming logic for logical signal expressions.
The available features are:
- AND.
- OR.
- Exclusive OR.
- NOT.
- COUNTERs.
- RS&D flip-flops.
Source: habr.com