The ATS scheme. ATS (automatic reserve input) for the generator

In the normal mode of power supply, the energy is provided by the power company and brought to the place of its use. When its main source ceases to function, the power from the second network input or the used backup generator must be manually or automatically supplied to the loads, for which the automatic transfer scheme (ATS) serves . Its main task is the redistribution of power from the power system to a backup power source.

III category of power supply reliability

As is known, power supply companies divide all their consumers, i.e. those persons (legal and physical) with which they conclude contracts for the supply of electricity, into three categories in terms of the reliability of electricity supply. The lowest reliability in the third category. Such a power customer is provided with only one three-phase input voltage of 6 or 10 kV (sometimes 400 V) or single-phase 230 V input from one supply substation, but the cost of connecting loads to the network in this category is minimal - it is enough to install a simple single-transform KTP and connect it with The nearest overhead transmission line.

Do I need an ATS scheme for the III category?

PUE allows the possibility of power supply under this scheme, if the power industry guarantees the restoration of power after accidents for not more than a day. And if it is not so? Then you need a backup power source, which is usually a benzo electric unit or diesel generator. In earlier times, consumers manually connected their loads to them and launched them into work. But as the automation of these products developed, it became possible to carry out their commissioning without human intervention.

And if it is possible to start the diesel generator automatically, then it is also possible to connect the loads of the consumer to it. So there was a modern concept of a two-in-water ATS, the electric circuit of which, shown below, is already becoming the standard of power supply for a private house.

II category: does she need an ATS

If a consumer orders two network power inputs, then it goes to the next category - the second. In this case, energy, as a rule, requires customers to pay for the construction of a two-transformer substation. In its simplest form, it contains two bus sections (these are simply aluminum or at best copper strips) of high voltage with their input switches, to each of which only one of the high voltage inputs (6 or 10 kV) is connected. Between the sections is located the so-called sectional switch. If it is open, then each high-voltage input can be powered by only one transformer (usually only one of the two is in operation, the second is in reserve - and this is also a typical requirement of power engineers). If there is a drop in voltage on one of the inputs, the customer's electrician can manually switch on the sectional switch and apply a load to the permanently operating transformer from another high-voltage input.

Such consumers, in fact, do not need AVR. However, in the last decade, energy companies often suggest that they install them in typical two-transformer substations on the low-voltage side. Such an ABP shield has two inputs from low-voltage windings of different transformers (they both must be energized, but only one of them is loaded at any time) and one output to low-voltage buses to which all loads are connected.

First category - AVP required

But if the customer in principle is not satisfied with the temporary delay in manually switching the inputs, then he is forced to use ATS without fail and move to the next category of power supply reliability - the first. In its simplest form, the circuit diagram of the ATS can contain two inputs from the same two sections of the buses of the substation and the switching unit of the sectional switch (usually vacuum). If the voltage disappears on the supply input, the automation cuts off its input switch and turns on the sectional switch. After that, the combined bus voltage comes from the second input. The two-input AVR in this case can also be implemented on the low-voltage side of the substation, as described above.

But from the consumers of the 1st category, the PUE allocates a so-called special group, which does not include enough two network power inputs, but it is also necessary to have a third backup input, usually performed from a diesel generator. In this case, an ATS is required for 3 entries. Its circuit is executed at low voltage.

How the ATS device with generator input works

Recently, many automatic backup devices with a microprocessor controller have appeared on the market. A great popularity in this regard is enjoyed by control relays-controllers of Easy series manufactured by Moeller. Analyzing the signals of the voltage sensors, the microcontroller detects a power failure and initiates the procedure for starting the generator motor (usually synchronous). Once it reaches the rated voltage and frequency, the control system switches to supplying the load to the consumer. From the point of view of electrical engineering, the connection scheme of ATS for critical and powerful loads is a rather complex task, since inevitable time delays and other technical difficulties make it difficult to instantly receive backup power.

Frequency and voltage monitoring

One of the main functions of the ATS device is to detect a voltage drop or a complete disappearance of the main power source. As a rule, all phases of the supply network are monitored on the side by means of a minimum voltage relay (phase-monitoring relay). The failure point is determined by the voltage drop below the minimum permissible level in any of the phases. The voltage and frequency information is transferred to the ATS shield, where it is possible to continue feeding the loads. The permissible minimum of voltage and frequency must necessarily be overcome before switching the loads to power from the backup generator, the power of which must provide it.

Basic time delay

The ATS circuit usually has the ability to broadly adjust the delay time for its operation. This is a necessary function for the ability to stop unjustified outages from the main power supply during short-term disturbances. The most prevalent time delay overrides any short-term trips, so as not to cause unnecessary starts of the generator drives and switching loads to them. This delay is in the range of 0 to 6 seconds, with one second being the most common option. It should be short, but sufficient to connect loads of consumers to backup power supplies. Many companies today are buying powerful uninterruptible power supplies with rechargeable batteries, which ensure a minimum connection delay time.

Additional time delays

After the main power is restored, some time delay is necessary to ensure sufficient load stability to disconnect it from the backup power. As a rule, it is from zero to thirty minutes. The ATS for the generator should automatically bypass this time delay in returning to the main source if the backup fails, and the main one again works normally.

The third most common time delay includes the period of engine cooling. On its length, the control system of the diesel generator controls the unloaded engine until it stops.

In most cases, it is usually desirable to switch loads to a standby generator as soon as the appropriate voltage and frequency levels are reached. However, in some situations, end-users want a sequence of switching different loads to the standby generator. When required, several ATS schemes for the generator operate with individual time delays, so that loads can be connected to the generator in any desired order.

The actuators of the reserve input circuits

The end result of the considered class of devices is the switching of electrical circuits, their switching from the main input to the reserve one. As it was mentioned above, in the electrical substations the ATS circuit can be realized both on the side of the higher and lower voltage. In the first case, its executive elements are regular high-voltage switches. In the second case, which includes switching loads to the generator input, switching is carried out by low-voltage devices.

They can either be part of the equipment of the switchboard (panel) of the ATS, or they can be external to it and be part of the general scheme of power supply to the loads. In the first case, it is possible to use magnetic starters - it is used in redundancy devices for non-industrial consumers at a power of their loads up to several tens of kW. At higher capacities, ATS is used on contactors. The schematic of the device in both cases is the same.

External low-voltage devices of reserve input circuits are power circuit-breakers with electromagnetic drives. The function of the actual ATS device is, in this case, reduced to the generation and delivery of corresponding on / off signals to them.

Typical AVR block for 3 entries. Scheme and algorithm of work

It is intended for the realization of continuous feeding of loads with a voltage of 0.4 kV from three power sources: two three-phase network inputs and three-phase input of a diesel generator. The executive devices are regular circuit breakers Q1, Q2 and Q3 of each of the inputs, which protect the loads of the 1st category of power supply reliability.

The algorithm of the block is as follows:

1. There is voltage on the main input. Then Q1 is on, and Q2 and Q3 are disabled.

2. There is no voltage at the main input, but on the backup one there is. Then Q2 is on, and Q1 and Q3 are disabled.

3. There is no voltage on the main and backup inputs. Then Q3 is on, and Q1 and Q2 are disabled.