Studies start circuit synchronous motor axial pump in power supply systems

Studies start circuit synchronous motor axial pump in power supply systems

Raksitullaeva D.I., Karimov R.Ch.

Annotation: The effect of the acceleration of the pump unit with an axial pump at start-up the reliability and quality of the pumping station unit. Proposed changes typical schemes starting synchronous motors that provide synchronization slip function and coasting angle of the rotor, which improves the starting conditions of the pump unit.

Keywords: Pump unit, the transition process, pumping stations, synchronous motor, pipeline.

Height of pumping irrigation area in recent years has led to the need to build a large number of major pump stations equipped with high-power pumping units. A characteristic feature of these pump units is the frequent change of modes for a given fluid loss schedule. Transients, even very short duration, reduce the reliability of pumping stations and worsen the conditions of their operation. Our studies modes of pumping units have identified the need to address transients in blocks of pumping stations.

The basic operational transients in blocks pumping stations occur during starting and stopping of pump units. These transients, repeated in accordance with the schedule of pumping stations (sometimes several times a day) cause significant dynamic loads on structural elements of pumping stations, units and reduce their operational reliability [1].

Modern large pump units with axial vertical pumps type ОPYu-185 and OP10-260 equipped with synchronous motors capacity of 5 MW and 12.5. Start of pump units accompanied interconnected electromechanical and hydrodynamic transients in blocks of pumping stations (synchronous motors - pump - pipeline)

Commonly used starter circuit synchronous motors Axial pumps (direct asynchronous start with the filing of the excitation current in the stator current function) [2] are selected for reasons of relatively low cost, given the potential of power supply network. It is believed that the combined use of the pump and synchronous motors does not provide for any restrictions to the trigger circuits. As a result of underestimation of the interconnectedness of transients in blocks pumping stations occurs unsatisfactory formation launchers hydrodynamic transients in the flow of the pump units and the deteriorating operating performance units.

Carried out in the years 2010-2016 field studies starting transients of pump units (pump type OP10-260; synchronous motors type VDS 375-130/24; N_n=12500 kW; U_n=10 kV; n_n=250 turnover/min, start emptying the pipeline) stage pump stations of the Amu-Zang trunk allowed to carry out their analysis and to identify the causes of poor flow trigger modes. As a result, according to research obtained by characterizing the change in the electrical and hydraulic parameters of pumping stations the unit at start-up (Fig. 1).

Start pumping units accompanied by a significant decrease in pressure in the impeller chamber (curve P₁), which is caused by the dynamic pressure component, which depends on the magnitude of the acceleration pump units. In the start-up period of pressure in the impeller chamber reaches for direct start synchronous motors 3.2 m. VS, which reduces the amount of stock kvitantsionnogo pump units to H_SV=6,5 m., VS The pressure at the beginning of the pipeline (curve P₂) increases rapidly, which is also due to the magnitude of acceleration.

Occurrence of pressure fluctuations in the pump chamber the impeller due to the effect of hydrodynamic transients amplified alternating change of acceleration of the rotation frequency. These oscillations occur before synchronizing the action of reactive torques from express rotor synchronous motors pole.

Figure 1.

Synchronize synchronous motors after the excitation current (curve i_b) and the output of pump units at the rated speed is accompanied by transient electromechanical retraction of the rotor synchronous motors in synchronism. This start-up phase differs increasing pressure pulsation in the flow of the pump units, which reaches a value below the impeller of 4,7 m., VS, and at the beginning of the pipeline 2,0 m. VS .; pressure fluctuations degrade hydrodynamic flow transients and formation flow.

The voltage on the tire pumping stations (curve U) at the initial start-up period falls to 0,7∙U_n, and inrush current reaches (curve I_s) its 5-fold value. Current and power consumption of synchronous motors after significant fluctuations due to retraction in synchronism, by the end of stage (t_n=14) drop to values that differ little from the steady operation mode for pumping units, and the voltage on the tires pumping stations is reduced to the nominal value.

When the pumping units with a rated speed filling of the discharge pipe is accompanied by small pulsations damped pressure in impeller chamber and at the beginning of the pipeline and increasing the static pressure of the water flow to approach the siphon outlet connections. Charging the overflow siphon it is characterized by water hammer in the pipeline, damped oscillations of pressure and power synchronous motors and repeated increase in the pressure pulsations.

After charging the overflow siphon installed operating pressure, pump flow, current and power synchronous motors. The pulsations of pressure in the pipeline are stored, and their value is set at a different identical launches pumping units, which can be explained hysteresis phenomena of hydrodynamic transients [3].

Analysis of starting transient pumping units shows that it is necessary to carry out "soft" start with a small and little-changing acceleration. Such start synchronous motors can provide a frequency control circuit and to some extent with the current-limiting circuit, and reactors for applying excitation current in synchronization function and the slip angle of the rotor run-out.

Opinion on the Non-Applicability "reactor" start pumping units emptying pressure conduit, is reflected in the literature [2] and to use the CMC, based on the malfunction of the control circuit supply excitation synchronous motors.

Carried out during the field research reactor starts to provide a reduction in the dynamic forces on the structural elements of the pumping units, an increase kvitantsionnogo stock by 16% compared to direct start and reduce pressure fluctuations during start pumping units at 26%, and in the steady state by 43%. Reactor start-up takes place "gently" without any shock and vibration.

Time reversal of pump units to speed-synchronous (t1) and the start time (to steady state) (t₂) is accordingly:

- For direct start synchronous motors t₁=9,3 and t₂=42 seconds;

- When the reactor t₁=13,6 and t₂=43 seconds.

Same starting time of pump units, despite the tightness of the turn at the reactor start-up, due to the reduction shear phenomena identified during prior field studies [4].

The magnitude of pressure fluctuations in the flow of the pump units at startup depends on the filing and the amount of current excitation synchronous motors when synchronizing. Applied to the Amu-Zang trunk starting synchronous motor control circuit to supply excitation current in the stator functions and definite time does not provide a sufficiently "smooth" synchronization of synchronous motors and increases the pressure fluctuations at the start.

The scheme proposed by us (Fig. 2) of the engine synchronization occurs on reaching favorable conditions depending on the moment of resistance (blade rotation angle) or to bypass the reactor, or after. A pulse on the supply of the excitation current (AC) to synchronize the engine is supplied to the sliding function (S) and the rotor angle overrun (Θ) using RPV Relay included in the part of the discharge resistor through the diode (D). The diode is connected so that the coil current flows around the RPI in the half-wave, when the induced voltage in the field winding synchronous motor has a reverse polarity with respect to the exciter voltage (V). Incorporation and the appropriate setting RPV allow file synchronization pulse at the instant when the optimal position of the rotor synchronous motors and implement it in sync with minimal vibrations.

Figure 2.

This scheme, in contrast to the known types of circuits fixed "light" or "heavy" starter, depending on the size of the resistive torque synchronous electric motor performs synchronization on a full or reduced voltage, providing the most "smooth" start synchronous motors.

Thus, the axial pump units in the pump stations units make high demands for schemes starting synchronous motors. This satisfies the requirements of the proposed scheme (Fig. 2), which provides a more reliable operation of the pumping stations.

REFERENCES

1. O.V.Zaharov et al. Experience of operation of large axial pumps on the main channels. -M .: Hydraulic Engineering, 1976.

2. N.N.Arshenevsky, B.B.Pospelov. Transients of large pumping stations. -M .: Energy, 1980.

3. V.Ya.Karelin. Cavitation phenomena in centrifugal and axial pumps. -M .: Mechanical Engineering, 1975.

4. Report NISaGidroproekta. Field investigations of pumping units to the siphon discharge outlets equipped with hydraulic devices for vacuum breakdown. -M .: 1978.