Auxiliary current systems in electrical substations
Purpose of the auxiliary current system of electrical substations
The set of feeders, cable lines, busbars for powering switching devices and other elements of operational circuits make up the current operation system of this electrical installation. The operating current in the substations is used to power secondary devices that include operational protection schemes, automation and telemechanics, equipment for remote control, emergency and warning signaling. In case of disturbances in the normal operation of the substation, the operating current is also used for emergency lighting and power supply of electric motors (especially critical mechanisms).
Design of installations for operating current
The design of the working current installation is reduced to the selection of the type of current, the calculation of the load, the selection of the type of power sources, the composition of the electric circuit of the working current network and the selection of the mode of operation.
Requirements for working current systems
Operating current systems require high reliability in the event of short circuits and other abnormal modes in the main current circuits.
Classification of operating current systems in electrical substations
The following current control systems are used at substations:
1) direct working current - a power supply system for working circuits, in which a battery is used as a power source;
2) alternating working current — the power system of working circuits in which the main power sources use measuring current transformers of protected connections, measuring voltage transformers and auxiliary transformers. Pre-charged capacitors are used as additional pulsed power supplies;
3) rectified operating current — the power supply system of operating circuits with alternating current, in which alternating current converted to DC (rectified) using power supplies and rectifier power supplies. Preloaded capacitors;
4) system with mixed working current — a system for powering working circuits in which different systems of working current (direct and rectified, alternating and rectified) are used.
In current operating systems, a distinction is made between:
- dependent power supply, when the operation of the power supply system of the working circuits depends on the operation mode of the given electrical installation (electrical sub-station);
- independent power supply, when the operation of the power supply system of the working circuits does not depend on the operation mode of the given electrical installation.
Application areas for different operating systems
Direct operating current is used in 110-220 kV substations with busbars of these voltages, in 35-220 kV substations without busbars at those voltages with electromagnetically operated oil switches, for which the possibility of inclusion by rectifiers is not confirmed by the manufacturer.
Alternating current is used in 35/6 (10) kV substations with 35 kV oil circuit breakers, in 35-220 / 6 (10) and 110-220 / 35/6 (10) kV substations without switches on the high voltage side. when the 6 (10) -35 kV circuit breakers are equipped with spring drives.
The rectified operating current applies: at 35/6 (10) kV substations with 35 kV oil circuit breakers, at 35-220 / 6 (10) kV and 110-220 / 35/6 (10) kV substations without switching on the high voltage side , when switches are equipped with electromagnetic drives; on 110 kV substations with a small number of oil circuit breakers on the 110 kV side.
A mixed direct current and rectified operating current system is used to reduce the capacity of the storage battery by using power rectifiers to power the solenoid circuits for switching oil switches. The feasibility of using this system must be confirmed by technical and economic calculations.
A mixed system of alternating and rectified operating current is used: for substations with alternating operating current, when they are installed at the power inputs of switches with an electromagnetic drive, to power the electromagnets on which rectifiers are installed. For 35-220 kV substations without switches on the high-voltage side, when reliable operation of the protection of feeders in the event of a three-phase short-circuit on the medium or high voltage side is not ensured.
In this case, the protection of the transformers is carried out on alternating current with the help of pre-charged capacitors, and the other elements of the substation - on rectified operating current.
Direct current system
Accumulator batteries of type SK or SN are used as sources of constant operating current.
DC users
All energy consumers powered by a storage battery can be divided into three groups:
1) Permanently switched on load - devices of control devices, interlocks, alarms and relay protection, permanently rationalized in current, as well as permanently switched on part of the emergency lighting. The constant load on the battery depends on the wattage of the always-on alarm and emergency lights and the type of relay. Since the permanent loads are small and do not affect the choice of the battery, it is possible in the calculations to roughly assume for large substations 110-500 kV the value of a permanently connected load of 25 A.
2) Live Load — occurs when AC power is lost during emergency operation — emergency lighting and DC motor load currents. The duration of this load is determined by the duration of the accident (estimated duration is 0.5 hours).
3) Short-term load (lasting no more than 5 s) is created by the currents for turning on and off the drives of circuit breakers and automatic machines, the starting currents of electric motors and the load currents of control devices, interlocks, signaling and relay protection, which for are briefly rationalized by the current.
AC operating current system
With AC operating current, the simplest way to supply tripping solenoids to the circuit breaker is to connect them directly to the secondary circuits of current transformers (direct-acting relay circuits or with tripping solenoids de-cycling). In this case, the limit values of currents and voltages in the current protection circuits must not exceed the permissible values, and the current cut-off electromagnets (relays of the RTM, RTV or TEO types) must provide the necessary protection sensitivity according to the requirements PUE… If these relays do not provide the required protection sensitivity, the interrupting circuits are powered by pre-charged capacitors.
At AC substations, the automation, control and signaling circuits are powered from the auxiliary busbars through voltage stabilizers.
Sources of alternating operating current are auxiliary transformers and transformers for measuring current and voltage, supplying secondary devices directly or through intermediate connections — power supplies, capacitor devices. AC operating current is distributed centrally and therefore does not require a complex and expensive distribution network. However, the dependence of the power supply of the secondary equipment on the presence of voltage in the main network, the insufficient power of the sources themselves (current measurement and voltage transformers) limit the range of working alternating current.
Current transformers serve as reliable sources to provide protection against short circuits; voltage transformers and auxiliary transformers can serve as sources of protection against faults and abnormal modes not accompanied by deep voltage drops when high voltage stability is not required and power interruptions are acceptable.
Voltage stabilizers are designed for:
1) maintenance of the necessary voltage of the working circuits during the operation of the AFC, when it is possible to reduce the frequency and voltage at the same time;
2) separation of the working circuits and the remaining auxiliary circuits of the substation (lighting, ventilation, welding, etc.), which significantly increases the reliability of the working circuits.
Fixed operating current system
The following are used for AC rectification:
Stabilized power supplies of type BPNS-2 together with current of type BPT-1002-for power supply of protection, automation, control circuits.
Unstabilized power supplies of the BPN-1002 type are used to power signaling and blocking circuits, which reduces the branching of the operating current circuits and provides the ability to supply all the power to the stabilized units for the protective operation and tripping of the circuit breakers.
BPN-1002 blocks instead of BPNS-2-for powering protection, automation, control circuits, when the possibility of their use is confirmed by calculation and stabilization of the operating voltage is not required (for example, in the absence of AFC).
UKP and UKPK powerful PM rectifiers with inductive storage - for powering the switching solenoids of oil switch drives.An inductive storage device ensures that the breaker is on short circuit with dependent power supply of switching circuits.
Unstabilized power sources BPZ-401 are used to charge capacitors, which are used to turn off separators, turn on short circuits, turn off 10 (6) kV switches with undervoltage protection, as well as turn off switches 35-110 kV when powering, the power supply unit is insufficient.
Read also: How high voltage disconnectors work and are arranged
Earlier on this thread: Handbook of electrical engineering / Electrical devices
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# 1 wrote: CJSC MPOTK Technokomplekt (7 Nov 2008 15:11)
AUOT-M2 series current control devices
AUOT-M2 devices are used in guaranteed power supply systems in facilities of the first category.
The devices are intended for:
• for continuous supply of consumers with a stabilized voltage standard 220V;
• for charging batteries connected separately or in buffer mode with a load;
• to ensure recharging of storage batteries connected separately or in buffer mode;
• monitor the condition of the batteries.
Technical characteristics of the AUOT-M2 series
Mains supply 380 V, -30% + 15% *
Operating frequency 50-60 Hz
Nominal constant output voltage of 60/110 / 220V
Rated output current 10/20/40 A
Maximum output current during operation of one power unit from 12 to 40A Maximum output current during parallel operation of power units from 20 to 70A
Maximum output power when operating one power unit from 1.7 to 10 kW
Maximum output power in parallel operation of power units from 2.9 to 17.5 kW
Output voltage adjustment ranges: 48V minimum, 250V maximum
The number of battery cells is from 30 to 102 pcs.
Control of the isolation of the consumer network from 5 to 50 kOhm
Output voltage ripple factor no more than 0.5%
Output voltage instability less than 0.5%
Efficiency not less than 0.95
Redundancy — two independent energy units;
— two inputs of the power network;
— AVR;
— battery included in buffer mode.
Control of the insulation of the consumer network 5-50 kOhm