Improved diesel engine start

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Improved diesel engine start

The article was published in the magazine "Locomotive" No. 2 (566) FEBRUARY 2004.
On serial diesel locomotives of domestic and foreign construction, the diesel engine is started by directly turning on the traction generator, which performs the function of a starter motor. The disadvantage of such a system is the high peak of the inrush current and the rapidity of its increase. Both phenomena accelerate the wear of the battery, and as it wears out, the reliability of starting the diesel engine decreases.

To eliminate this shortcoming, industry and transport specialists are developing a wide variety of technical solutions to reduce the inrush current of starter motors. The Gorky-Sortirovochny depot of the Gorky Road also recently tested a device for electric starter start of a diesel engine on a CHME3 diesel locomotive. It is a discrete-acting voltage regulator. The idea was borrowed from a traction battery electric drive and developed following the requirements of operation in the mode of electric start-up of a diesel engine.

The electrical diagram of the new electric starter start system for diesel locomotives is shown in Fig. 1. A discrete voltage regulator is added to the standard elements, consisting of a short-circuit contactor of diodes VD1 and VD2, a current relay KA and a resistor R. A discrete voltage regulator is used for two-stage regulation of the voltage supplied to the generator armature G.

The regulator operates during the diesel start-up process as follows. Preparation for start-up begins by closing the contacts of the battery switch Q. In this case, the half-sections of the GB battery are connected in parallel, since contact K3.2 of the short circuit contactor is open. The VD1 diode connects the positive terminals of the AB half—sections, and the VD2 diode connects the negative ones.

The AB voltage is equal to half of the rated voltage. Under the action of this voltage, the current from the "plus" AB passes through the upper contact of the switch Q, the opening contact K3.1 of the contactor K3, the retracting coil of this contactor, the opening contact KA.1 of the current relay KA, the contact of the switch Q to the "minus" AB. Contactor K3 is designed to be switched on at a voltage equal to half the rated voltage of the battery. Its contact K3.2 connects the half-sections of the battery in series, and its voltage increases to the nominal value.

Contact K3.1 of contactor K3 is opened by inserting resistor R into the circuit of its coil. The electric circuits of the locomotive are put under the rated voltage. Preparations for the diesel engine start-up have been completed. The start starts by pressing the start button. All devices providing pre-start oil pumping, as well as the starting contactor K1, are put into operation. After the time allotted for pumping the oil has elapsed, the contactor K2 is switched on.

The battery current is supplied to the armature of the traction generator G, which performs the function of a starter motor, the windings LG1, LG2 of the generator and to the current relay KA. It turns on, and its contact KA.1 in the contactor circuit K3 breaks this circuit. Contactor K3 turns off, and its contact K3.2 switches the AB half-sections to a parallel connection. The start of the starter motor G takes place at reduced voltage and current values. As the speed increases, the opposite EMF of the armature increases, and its current decreases.

Simultaneously with an increase in the rotational speed of the diesel generator shaft, the voltage of the auxiliary generator connected by a V-belt transmission to the generator shaft increases. A voltage relay KU is connected to its armature. This relay is activated at such a speed of rotation of the shaft of the diesel generator, when the armature current of the generator G decreases to the same value that corresponded to the start of the start. In this case, the contact of this relay KU creates a bypass circuit for the passage of current into the coil K3.

The short circuit contactor is switched on again and, as already described, transfers the AB half-sections to a serial connection. The full battery voltage is applied to the generator armature G, and the frequency of rotation of its shaft continues to increase. At a certain value, the diesel starts. The standard start-up system disconnects the generator from the AB by opening the contacts of the starting contactors K1 and K2.

Diesel engine start-up using a discrete voltage regulator was tested on CHMEZ diesel locomotives No. 3475 and 1855. The peak starting current of the battery, according to commission tests, decreased from 1600 to 650-700 A. In Fig. 2 shows graphs reflecting the electric starter start of a diesel engine on a CHMEZ diesel locomotive using a discrete voltage regulator with sequential excitation of a generator G operating in starter motor mode.

When the generator is turned on at full battery voltage (90 V), the armature current Ia and the battery current IB increase. However, at a current of about 100 A, the KA current relay is triggered, ensuring that the battery switches to parallel half-sections. Currents Ia and IB are separated, and the total current of the two half-sections increases to a peak value and becomes equal to the armature current Ia = 1350 A. The battery voltage at 45 V EMF sections decreases to 30 V in the "dip" and gradually recovers as the 1B currents decrease.
When the angular rotation speed of the diesel generator shaft reaches a value of w = 12 rad/s (n = 115 rpm), the KU relay is switched on, ensuring switching of the AB half-sections to sequential operation. The battery current, now equal to the armature current, increases abruptly to 700 A, and the rotation frequency of the shaft increases to 15 rad/s (n = 143 rpm). At this speed, the diesel engine starts.

Further, the value of y increases sharply, after which the regulator outputs the diesel engine to an idle speed of n = 350 rpm. The low-voltage start of the generator G lasts only 1.1 seconds. This is enough for the EMF of the generator to reach a value that limits the armature current to 700 A at the rated EMF of the battery.

The presented device, in addition to the field-tested voltage regulator, contains an excitation current regulator for the independent winding LG3 of the generator G. It consists of a current sensor and its 1a derivative, as well as an UZ converter. This regulator is inserted into the electric starter device of the diesel engine in order to enhance the magnetic flux, and therefore to further reduce the armature current 1a, to protect against reverse current after starting the diesel engine.

The UZ converter prevents the demagnetizing effect of the EMF, which is induced in the independent winding LG3. The initial value of the current Ie is regulated by the setpoint voltage Uy.

By simulating the start-up process of the generator G, which is equipped with a voltage regulator and a current regulator of the independent excitation winding, it was found that the armature current decreases from 650-700 to 325-350 A. This not only improves the reliability of starting the diesel engine and saves battery life, but also creates the prospect of using cheaper batteries with lower capacity.

Candidate of Technical Sciences E. S. YERILIN,
engineers A. S. REPIN, I. V. SYCHUSHKIN,
Doctor of Technical Sciences E. B. SHUMKOV, employees of the Nizhny Novgorod branch of VNIIZHTA

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