SU117667A1 - Device for automatic unloading of synchronous machines when they are overloaded - Google Patents

Description

A device is proposed for automatically unloading synchronous machines when they are overloaded.

The disadvantage of the known devices of the same purpose, in which the excitation system of the machine is affected by induction

time delay relay is a time delay mismatch

the required dependence defined by the expression t GGHz :, where C is a coefficient,

/ „- nominal current value

K is the ratio of the actual value of the current to the nominal.

In order to obtain a device that meets the requirements, it is proposed to perform a relay with a time delay proportional to the difference of the squares of the actual and specified current values of the machine and equal to the duration of its heating to an acceptable value for all values of overload.

The relay is made with two magnetic cores, powering them, each with two windings, powered by one current of a constant value proportional to the specified (nominal) current value of the machine, and the other current proportional to the actual current value of the machine, and creating magnetic fluxes directed in one the magnetic core is opposite, and in the other - according to.

In order to ensure the independence of the characteristics of the relay from the power factor of the machine, it is proposed to switch the relay coil powered by a current proportional to the actual value of the current of the machine through a magnetic amplifier powered by the same voltage regulator from which the second coil of the relay is powered.

The impact on the excitation system to return it to its original position with the disappearance of the conditions that caused the machine to overload is accomplished by an additional contact in the relay, closing with delay time when the actual current decreases to a value less than the specified current.

FIG. 1 shows the circuit of the automatic unloading relay; on

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№ 117667

FIG. 2 is a schematic of a contact relay system; in fig. 3 is a schematic diagram of an unloading device using this relay. The aforesaid HRD relay (FIG. 1), which is the main element of the device for the automatic unloading of synchronous machines when they are overloaded, simultaneously performs the functions of a measuring organ and a time delay organ. The relay is made on the basis of an induction single-phase counter with two magnetic conductors each carrying two windings, one of which flows around a current proportional to the actual value of the current, and the other current corresponding to the nominal value of the generator current. The direction of the current is chosen such that in one magnetic circuit the resulting flux is determined by the sum, in the other, by the difference between the real 1 and the nominal values of the generator current.

The moment acting on the disk relay is determined by the product of the fluxes of both systems and, consequently, by the difference of the squares of the real and nominal values of the generator current

M L (/, 2- / «), where L is a constant coefficient.

A moving contact 1 is attached to the moving relay system (Fig. 2), namely to the last gear of the gear, the rotation angle of which is determined from the expression:

8 -ig C, Mt C, L (/ 2 - / H-t C, () t,

where: Ci is a constant coefficient,

K is the frequency ratio of the generator overheating, V is the rotational speed of the moving contact.

As is known, the amount of heat released by the generator windings depending on the load is determined by the expression:

Q () -t, coinciding with the above expression.

The initial permissible value is taken as the amount of heat released when the generator is operated with 1.5 times overload for 2 minutes. In line with this, the angle of rotation of the movable contact of the relay from the initial to the final position is equal to the one that passes the contact in 2 minutes. with a current ratio of 1.5.

At small overload multiplications (, 2 and lower), taking into account the heat exchange process, allow large values of the overload time compared with the time obtained from the last expression.

As can be seen from the diagram of the device shown in FIG. 3, the relay windings, streamlined by a current proportional to the nominal value of the current of the machine, are fed from the voltage regulator CH through a transformer T and choke D. the same voltage regulator CH.

In order to increase the time of the relay at low overloads, it is assumed that the current in the relay coil is not proportional to the generator current up to a multiplicity of 1.2. This is achieved by appropriately selecting the operating point on the characteristic of the magnetic amplifier MU. The magnetic amplifier also serves to reduce the load on the current transformer of the generator PT, to eliminate the effect on the operation of the generator power factor relay load, to be able to maintain the generator unloading when the rotor current overloads and to prevent the relay from acting falsely when the power supply of the circuit disappears.

The latter is very significant and is achieved by the fact that in the presence of a magnetic amplifier, the relay coils are powered from one common source. In this case, the disappearance of the power supply can only lead to a failure of the relay, but not to a false action in the absence of an overload.

The inductor D serves to compensate for the angle between the currents in the relay windings, as well as to reduce the mutual influence between the windings located on the same magnetic core.

The proposed device for automatic unloading can be used both when the stator is overloaded and when the rotor is overloaded by the machine. For this purpose, a voltage proportional to the rotor current is applied to the same control winding of the magnetic amplifier, to which a voltage is applied proportional to the stator current. The current in the winding is determined by the T0: com (stator or rotor), the overload ratio of which is greater.

In the automatic unloading relay, except for one moving contact /, there are three fixed contacts 2, 3, 4 (Fig. 2).

During normal generator operation, with no overload, the moving contact 1 is in the closed position with contact 2.

When a generator overload occurs, the relay disk begins to vra, counter clockwise, after the time has elapsed, its available overload ratio, the moving contact / closes with contact 3. In this case, the intermediate relay is pulsed to unload the generator by reducing excitation current.

As soon as the stator (or rotor) current becomes equal to the nominal value (the return coefficient of the relay is close to unity), the contacts / and 5 are opened and the pulse to decrease the excitation current is stopped.

Prn current, less than the nominal, the relay disk receives a negative moment and begins vrashat in the opposite direction with Sko; rusti, hung w, it on the degree of underload of the generator.

Moving contact / after the time has elapsed, which corresponds to its multiplicity of underloading, approaches contact 2, I have an elastic spring. If the conditions that caused the machine to overload (for example, lower voltage in the network) are not completely eliminated, then the negative moment is small. The moving contact 1 cannot overcome the counteraction of the spring of contact 2, and contacts 2 and 4 do not close.

When I | ч conditions of the overload, the generator is unloaded more, the negative moment rises, the spring force is overcome, the contacts 2-4 are closed and a pulse is given to increase the excitation current - the pulse stops or when the generator current reaches its nominal value (contacts 2 and 4 open ), or when returning the installation device to its original optimal position.

In the described scheme, it is assumed that the installation device, which is affected by the automatic unloading relay, is not operational and under normal conditions, in the absence of overload, is in a certain position.

Subject invention

Claims (3)

1. Device for automatic unloading of synchronous machines when they are overloaded, containing its induction relay with an extra time effecting it on the excitation system of the machine, characterized in that, in order to obtain a time delay proportional to the difference of the squares of the actual and specified current values of the machine equal to the duration of its heating up to the permissible value for all values of the overload, the relay is made with two magnetic conductors, each of them is wired in two windings, fed by one current of constant magnitude, proportional to cial predetermined value current machine, and the other - a current proportional to the current actual value of the machine, to generate magnetic fluxes directed opposite to one magnetic circuit and in the other - according to. - 3 - № 117667 2.Supply | STVO of claim 1, characterized in that, in order to ensure the independence of the relay characteristic from the power factor of the mashiny, the relay winding, supplied with a current proportional to the actual value of the maschine's current, is connected through a magnetic amplifier powered by the same voltage stabilizer from which the second winding of the relay is powered. 3. The device according to paragraphs. 1 and 2, characterized in that, in order to act on the excitation system to return to its original position when the conditions causing overload of the mask disappear, an additional contact is provided to the relay, closing with a time delay when the actual current decreases to a value less than the specified current.