RU2319271C1 - Protective unit-board (versions) - Google Patents

Abstract

FIELD: protection of motor.

SUBSTANCE: winding of starter and ancillary relay are connected to all three phases behind terminals of starter. To start the device there is additional winding or double-terminal closing "start' button. Increased sensitivity of heat protection is provided by shunting of the button during starting. Increased speed of operation of electromagnet starter is provided by fact that its contact is not involved in operation during process of starting.

EFFECT: improved sensitivity; higher speed of operation.

9 cl, 3 dwg

Description

The invention relates to electrical engineering.

Known magnetic starters, the disadvantage of which is that they allow the operation of a three-phase electric motor in the absence of one of the phases.

Known "Relay device" / a.s. USSR No. 775783, MKI H01H 51/04 dated 07/31/78, /, which protects the load when the power supply is out of phase. However, it is difficult, expensive, has large dimensions, requires precise adjustment / hence, unreliable /.

Practice has shown that in about 75% of cases of engine failure, the cause is in-phase power. In turn, approximately 90% of cases of out-of-phase operation of engines occur for reasons related to the supply infrastructure - malfunction of circuit breakers, automatic machines, inserts, terminal blocks, transformers and sections of cable and overhead lines between them. The remaining 10% is distributed as follows: 9% is the fault of the starter / burning of contacts, faults of the kinematics / and only 1% is the fault of the cable between the starter and the motor.

Thus, if you control the secondary voltage - the voltage after the contacts of the starter itself, it is possible to prevent in 90% of cases the motor failure for this reason.

I invented the "Magnetic starter", carrying out this function / cm. Application No. 2005113014 / 09-015008, which issued a positive decision. It consists of two or three contactors, mutually interlocking each other with their power contacts. However, trying to introduce it into production, I was faced with the reluctance of manufacturers to change anything in their products. Therefore, I have developed this protective block remote control / hereinafter referred to as CBP /, based on the usual three-contact starter with minimal changes / coil / or without them at all. The prototype is / 1 /.

Option 1 of the ACB is a three-contact electromagnetic starter and an auxiliary relay connected to all three phases after the contacts of the starter. The starter has two common-mode windings, starting and holding. The launcher is connected to the contacts of the starter, and the holding - after them. Moreover, the holding winding is blocked in series with the make contact of the auxiliary relay.

To control the electric motor, two sub-options are possible:

Sub-option 1a: The start button is sequentially connected to the start winding circuit, and the stop button is sequentially connected to the holding winding circuit.

Sub-option 1b: The start winding is connected to two phases through a three-position switch with self-resetting / toggle switch /, which can turn it in antiphase to the holding winding. In this case, one of the phases is taken after the power contact of the starter, so that after the termination of the holding winding, the antiphase action of the starting winding, which in this option would be more correctly called the stop-start or control, would cease simultaneously.

It is necessary that the magnetic fluxes of the windings be approximately equal in magnitude, and taking into account the attenuating effect of the symmetric diode thyristor / cm. below/.

Option 2 of the ACB consists of a conventional starter and an auxiliary relay connected after the power contacts of the starter. To enable the motor to start, there is a two-contact “Start” button, one of the contacts of which shunts the power contact of the starter, and the second forms a bypass circuit with the other power contact of the starter together with the auxiliary relay connected in series / so that the load motors for the buttons do not start in phase / . The engine is preferably connected in a triangle.

Since one of the contacts of the Start button shunts the power contact, it passes part of the starting current. But since this happens within a short period of time / 0.5 ÷ 2 sec /, and the button opens, being shunted, a significant overload of the button is permissible in comparison with its nominal value.

For high power motors and star-connected motors, the auxiliary relay contact can be included in both shunt circuits. To enable the engine to stop, the Stop stop button is sequentially connected to any circuit.

If one of the phases in the network disappears or one of the contacts of the starter fails, the voltage on this wire does not disappear at all, but remains approximately equal to half the phase-to-phase due to the flow of current through the motor windings and induced EMF. This may be sufficient to keep the contacts in the closed position, therefore, the holding or the only windings of the starter and relay are connected through sequential symmetrical diode thyristors. The voltage of self-switching / breakdown / thyristors should be slightly higher than half of the interphase, multiplied by the sinusoid shape factor 1.571 / te. for a 220/380 V network, approximately 550 V /, and the holding current of the thyristors should be less than the operating current of the corresponding winding. That is, thyristors, cutting off the voltage below 350 V, will not pass half the voltage to the contactor windings and at the same time will ensure the effective operation of the windings at full voltage. The windings must be designed for the remaining voltage, which, depending on the breakdown voltage and the holding current, will be approximately 75-35% of the full / i.e. approximately 305 V /.

To protect the motor from overload, the circuit usually includes a protective element / circuit breaker, thermal relay /, opening all three phases. The presence of phase protection in the proposed BSS allows to simplify this task / it was also one of the objectives of the present invention / - it is possible to arrange the protective element in only one phase, and therefore it can be simpler and cheaper, for example, fuse-link.

In addition, option 2 provides another advantage over analogs: if you place the protective element in the circuit of the power contact shunted by the "Start" button, then at the time of pressing the button, the current flowing through the protective element will be only a fraction / approximately 50% / starting current, which, as you know, is several times more than the working one. And therefore, the security element may have a higher sensitivity.

Due to the fact that the starting current is several times higher than the rated current, the protective element is usually tuned to an even higher current and therefore does not protect the motor well from overload, even taking into account the increase in its sensitivity in option 2 of the air conditioner. The fact is that the electric motor is heated unevenly during overload, and the weakest section of the winding in terms of conductivity, in thermal and insulation terms, has time to burn out before the protection trips.

For high-speed motor protection, this CBP has an electromagnetic current limiter with an NC contact, which can be set to a current that is only slightly more than the rated current.

Since this limiter trips during start-up, in order to make it possible to start, the open contact of the limiter must directly or indirectly / i.e. functionally / bypassed with the ″ Start ″ button, which at start-up must be kept pressed until the electric motor reaches its rated speed. In this ACB, the NC contact of the current limiter is connected in series with the auxiliary relay.

This BSP can be used for both local and remote control of the electric motor. In the latter case, the remote start buttons are connected in parallel with the existing ones, and the remote "Stop" button is connected in series with the existing one. A five-wire / five-wire / cable line is required. When using the ACB in automatic control systems, the ACS contacts are connected as external buttons, and the start and stop pulses must be supplied through a time relay with self-resetting to the initial position.

Figure 1 shows a sub-option 1a of the BSS, where A, B, C are phases, D is an electric motor, PO and UO are the starting and holding windings of the starter, P is an auxiliary relay, KP and KS are the Start and Stop buttons, C1 and C2 are symmetric diode thyristors.

Figure 2 shows a sub-option 1B of the BSS, where T is the switch.

Figure 3 shows the option 2 of the BSP, where KPa and KPb - two-contact "Start" button, P - winding of the starter, Pr - protective element / fuse /, OT - electromagnetic current limiter.

The CBP in Fig. 3 works like this: when the two-contact button KPA-KPb is closed, the contact in phase C and the protective element Pr are bridged, and the contact in phase B is bridged by an open KPa circuit - contact R. In this case, the voltage is supplied to the starter winding P through KS and C2 . Power contacts are closed. Inrush current passes through the current limiter OT, and its contact opens, de-energizing relay P. The open contact P prevents the starter from self-locking, and therefore the Start button must be held for 0.5-2 s until the engine reaches its rated speed. When the current through the motor decreases to the rated value, the OT contact closes, the relay P trips and closes the contact P. The starter will be connected to phases D and C after its contacts. The start button can be released.

To stop the engine, it is enough to open the starter winding circuit using the COP button.

If, for any reason, the voltage in one of the phases disappears, the voltage on this conductor will decrease by about half, and the current through the symmetric diode thyristor C1 or C2 will not go. Either the starter winding is de-energized, or the relay winding first, and then the starter. The engine will disconnect from the mains.

During overload, the OT current limiter will trip, relay P will be de-energized, the starter will trip. Or the protective element Pr.

The use of an ACB will virtually eliminate the failure of electric motors due to in-phase supply or overload.

/ 1 / "Relay device", a.s. No. 775783 dated 07/31/78 H01H 52/04.

Claims (8)

1. A protective remote control unit, consisting of a three-contact electromagnetic starter and an auxiliary relay connected to three phases, characterized in that the starter has two common-mode windings - a starting and a holding one, the starting winding connected to the contacts of the starter, and the holding winding and connected in series with it auxiliary relay connected after starter contacts. 2. The remote control according to claim 1, characterized in that the start button is included in the start winding circuit, and the stop button is included in the holding winding circuit. 3. The remote control according to claim 1, characterized in that the starting winding is connected to two phases through a three-position switch with self-resetting with the possibility of changing its beginning, and to one of the phases after the contact of the starter. 4. The remote control according to claim 1, characterized in that the auxiliary relay and the holding winding of the starter are connected in series with symmetric diode thyristors. 5. The protective remote control unit, consisting of a three-contact electromagnetic starter and an auxiliary relay connected to the three phases, characterized in that the starter winding and the auxiliary relay are connected after the starter contacts, moreover, one contact of the starter is bridged by the contact of the two-contact start button, and the second contact of the starter it is shunted by a circuit from the second contact of the two-contact start button and the auxiliary relay connected in series with it. 6. The remote control according to claim 5, characterized in that the auxiliary relay and the sole or holding winding of the starter are connected in series with symmetric diode thyristors. 7. The remote control according to claim 5, characterized in that a safety element is included in the power section of the phase circuit shunted by the contact of the two-contact start button. 8. The remote control according to claim 5, characterized in that the current winding of the electromagnetic current limiter is included in the power circuit of one of the phases, the opening contact of which is connected in series with the auxiliary relay or in series with the starter block contact.

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