Armature constant

E = applied voltage, V V = counterelectromotive force (generated voltage), V R = armature resistance, H I = armature current, A k = constant dependent on motor design n = speed, r/min ( ) = magnetic-field flux... 

Remain constant for speed variations within the required speed N, as the field current is kept fixed and only the armature voltage is varied. For speed variations beyond N. however, when the armature voltage is kept constant and the field current is varied, the magnetizing losses afso vary... 

Fig. 4.14 DC servo-motor under armature control, e it) = Armature excitation voltage e it) = Backemf /a(t) = Armature current = Armature resistance = Armature inductance 6f = Constant field voltage if = Constant field current Tm = Torgue developed by motor 6 t) = Shaft angular displacement u] t) = Shaft angular velocity = dd/dt.

Constant-speed motors are usually suited for a speed range of less than 3 to 1 by field control, but mechanical and electrical characteristics govern maximum safe speeds. With constant voltage on the armature, as the field is weakened the speed increases and the motor develops constant horsepower. 

With an adjustable voltage supply to the armature, at speeds below basic, the motor is suitable for a constant-torque drive. Minimum speeds are limited by temperature rise, because the motor carries full-load current at the lower speeds and at low speeds... 

Speed adjuslmeiU from base speed downward is obtained by armature voltage control. The armalure current and torque in this range is limited by the thyristor ratings or motor temperature rise. Control above base speed at constant horsepower is obtained by field weakening. An example system is shown in Figure. 3-17a. In this... 

With field current control, the speed of a DC motor can be increased beyond its nominal speed by field weakening. Because voltage thereby remains constant at the armature, the latter is not suitable for actual speed feedback in the field suppression range. 

An alternate arrangement that would relocate the force gage from the shaker armature to the driven sample block could be advantageous, provided that the force gage sensitivity remains constant over the required temperature range. This relocation would eliminate the need to take account of the mass correction term, in the reduction of data. Instead, this mass loading... 

Constant speed direct-current motors are usually started by decreasing the amount of an external resistance in the armature circuit. The starting current may exceed full-load current by about 50 per cent. From 15 to 30 sec. should be allowed to bring a motor up to speed. This may be insured by automatic operation. The rheostat may incorporate low-voltage and overload releases, and should contain the motor-field circuit closing mechanism. Ordinary rheostats (starters) cost from 3 to 6 per cent as much as motors, the smaller sizes costing relatively more. 

The above expression is adequate for data that are typically available for the industry. The armature resistance Ra is only present in the time constant Ta. (Krause offers a more complete solution in which the omission of Ra is minimised. The effect is then to modify the time constant Ta... 

Figure 20.4 Short-circuit current decrement for a 2500 kW and a 37 kW induction motor. These motors have a relatively high armature time constant Ta that causes the initial offset of the waveform. The deep bar effect in the rotor has been taken into account.

The relay coil 185 operates a relay armature 188 that 60 tained substantially constant. If desired, any of the... 

Relay coil 206 then operates to cause armature 210 to connect with contact 215, thus reversing the motor 221 to drive the control rod into the reactor to a point where the neutron density starts to decay. The control rod 90, gg will thereafter hunt between a point above the balance position where the neutron density rises, and a point below the balance position where the neutron density decays, thus providing an average neutron density within the reactor as determined by the setting of slider 203 on resistor 205. As the mass of the reactor causes any temperature change to lag behind any neutron density change, the temperature of the reactor is maintained substantially constant. If desired, any of the well-known anti-hunting circuits may be utilized, as will be apparent to those... 

In the case of constantly fluxed synchronous motors, the stator cmrent will follow the motor torque more closely. After adding excitation losses, the synchronous motor efficiency is still shghtly better than the induction motor. The drive inverter for a synchronous motor supplies the armature or torque producing current, compared to the induction motor apph-cation where the inverter must supply torque producing current and magnetising current In the synchronous motor application, the motor operates at unity power factor, which reduces current demand in the inverter section. As a result, there are fewer losses in the inverter and motor, and to a lesser extent fewer losses in the converter. 

When a universal motor is run on direct current, the magnetic poles in the armature change while those of the field magnet remain constant. 

Several out-of-pUe mock-up expoiments have been conducted to demonstrate performances on holding force, response time, thermal endurance test under sodium, and measures against particle accumulation on the magnetic surface. The transient response tests with simulated ATWS conditions confirmed the time constant of the armature. In addition to the out-of-pUe tests, in-pUe mock-up and matmal expoiments were conducted in JOYO (Nakanishi et aL, 2010 Fujita et aL, 2011). The control rod holding stability imder the actual reactor-operational enviromnent was successfully confirmed. 

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