DYNAMIC BREAKING OF SPLIT PHASE MOTORS

The principle of dynamic breaking discussed earlier in connection with poly phase induction motors, also applies well to split phase motors. The procedure, as already explained, is to disconnect the stator windings from ac supply while the motor is running and instead, connect dc supply across the windings. Full wave rectifier is used to obtain dc supply from the available ac source. Precaution must be taken to avoid, simultaneous energization of the stator windings from both ac as well as dc supply. This is taken care of by providing electrical and/or mechanical interlocking of the contactors. A rheostat is provided in the dc circuit to control the time required for the motor to stop. Less is the value of rehostatic value of resistance, more quickly will the rotational energy get converted to electrical energy and get dissipated as heat and hence less will be the time required for the motor to stop. The control diagram for dynamic breaking of a split phase motor is shown in Figure.

Figure: Control circuit for dynamic breaking of a split phase induction motor

When the STOP-push button is pressed, contactor M gets de-energized and closes its contact M₂. Contactor DB gets energized through the back contact of the STOP-push button, closed contact TR₂ and contact M₂. Timer TR also gets energized along with contactor DB. The instantaneous contact of relay TR, i.e, TR₁ closes and thus both contactor DB and relay TR remain energized. Contactor DB energizes a bridge rectifier which feeds dc current into the stator winding of the motor. Current to be fed is adjustable through a rheostat, R. Due to feeding of dc current the motor slows down and comes to a quick stop. After a pre-set delay which would match with the time taken by the motor to stop, the timer TR operates and opens its delayed contact TR₂ and thus de-energizes contactor DB and gets reset. The time allowed to stop the motor, as explained earlier, can be varied by adjusting the rheostat R.

Comments

PRIMARY SECONDARY AND TERTIARY FREQUENCY CONTROL IN POWER SYSTEMS

Primary, Secondary and Tertiary Frequency Control in Power Systems Author: Engr. Aneel Kumar Keywords: frequency control, primary frequency control, automatic generation control (AGC), tertiary control, load-frequency control, grid stability. Frequency control keeps the power grid stable by balancing generation and load. When generation and demand drift apart, system frequency moves away from its nominal value (50 or 60 Hz). Grids rely on three hierarchical control layers — Primary , Secondary (AGC), and Tertiary — to arrest frequency deviation, restore the set-point and optimize generation dispatch. Related: Power System Stability — causes & mitigation Overview of primary, secondary and tertiary frequency control in power systems. ⚡ Primary Frequency Control (Droop Control) Primary control is a fast, local response implemented by generator governors (dro...

CASCADED TRANSFORMERS METHOD FOR GENERATING AC HIGH VOLTAGE

High-Frequency AC High Voltage Generation Using Cascaded Transformers Author: Engr. Aneel Kumar Figure 1: Infographic representation of cascaded transformers method for generating high AC voltages. Introduction In high voltage engineering , generating very high alternating current (AC) voltages is essential for testing equipment like insulators, circuit breakers, power cables, and other apparatus. One common and effective method for producing such voltages is the cascaded transformers method . This technique uses a series connection of specially designed test transformers , where the secondary of one transformer feeds the primary of the next. In this way, voltages are built up step by step, achieving levels in the range of hundreds of kilovolts (kV) or even megavolts (MV). Working Principle The principle of cascaded connection relies on the fact that each...

ADVANTAGES AND DISADVANTAGES OF CORONA EFFECT IN TRANSMISSION LINES | ELECTRICAL ENGINEERING GUIDE

Advantages and Disadvantages of Corona Effect in Power Systems In high-voltage overhead transmission lines , the corona effect plays a critical role in system performance. Corona occurs when the air around a conductor becomes ionized due to high electric stress. While often seen as a drawback because of power losses and interference , it also provides certain engineering benefits . This article explains the advantages and disadvantages of corona effect in detail, with examples relevant to modern electrical power systems. ✅ Advantages of Corona Effect Increase in Virtual Conductor Diameter Due to corona formation, the surrounding air becomes partially conductive, increasing the virtual diameter of the conductor. This reduces electrostatic stress between conductors and minimizes insulation breakdown risks. Related Reading: Electrostatic Fields in High Voltage Engineering Reduction of Transient Surges Corona acts like a natural cushion for sudden ...

REVERSING DIRECTION OF ROTATION OF UNIVERSAL MOTOR

The direction of rotation of a universal motor can be changed by either: (i) Reversing the field connection with respect to those of armature; or (ii) By using two field windings wound on the core in opposite directions so that the one connected in series with armature gives clockwise rotation, while the other in series with the armature gives counterclockwise rotation. The second method, i.e, the two field method is used in applications such as motor operated rheostats and servo systems. This method has somewhat simpler connections than the first method. For simple applications like portable drills etc. manual switches are frequently used for reversing the direction of rotation of the motor. Figure 1 (a and b) shows how a DPDT (Double Pole Double Throw) switch and a three position switch may be used for reversing the direction of rotation of single field and double field type of motors respectively. Figure 1 Reversing of a universal motor (a) Armature re...

Advantages of Per Unit System in Power System Analysis | Electrical Engineering

Advantages of Per Unit System in Power System Analysis In electrical power engineering, the per unit (p.u.) system is one of the most widely used techniques for analyzing and modeling power systems. It is a method of expressing electrical quantities — such as voltage, current, power, and impedance — as fractions of chosen base values rather than their actual numerical magnitudes. This normalization technique provides a universal language for system calculations, minimizing errors, simplifying transformer modeling, and enabling consistency across multiple voltage levels. Because of these benefits, the per unit system is essential in fault analysis, load flow studies, transformer testing, and short-circuit calculations . ⚡ What is the Per Unit System? The per unit system is defined as: Q u a n t i t y ( p u ) = A c t u a l V a l u e B a s e V a l u e Quantity_{(pu)} = \dfrac{Actual \ Value}{Base \ Value} Q u an t i t y ( p u ) = B a se ...

PRINCIPLE OF OPERATION OF UNIFIED POWER FLOW CONTROLLER UPFC

UPFC consist of two back to back converters named VSC1 and VSC2, are operated from a DC link provided by a dc storage capacitor. These arrangements operate as an ideal ac to ac converter in which the real power can freely flow either in direction between the ac terminals of the two converts and each converter can independently generate or absorb reactive power as its own ac output terminal. Figure: Basic UPFC scheme One VSC is connected to in shunt to the transmission line via a shunt transformer and other one is connected in series through a series transformer. The DC terminal of two VSCs is coupled and this creates a path for active power exchange between the converters. VSC provide the main function of UPFC by injecting a voltage with controllable magnitude and phase angle in series with the line via an injection transformer. This injected voltage act as a synchronous ac voltage source. The transmission line current flows through this voltage source resulting in reactive an...

Types of Transmission Towers in Saudi Electricity Company (SEC) – NGSA Standards

The Kingdom of Saudi Arabia (KSA) is rapidly expanding its energy infrastructure projects to meet the growing demand for electricity. At the heart of this growth lies the high voltage transmission network , which delivers reliable power from generation plants to cities, industries, and remote areas. To ensure safety and efficiency, the Saudi Electricity Company (SEC) follows strict NGSA (National Grid Saudi Arabia) standards for designing and selecting transmission towers . These lattice steel towers are engineered to withstand extreme desert conditions, high wind loads, and long transmission spans. In this article, we will explore the different types of transmission towers in Saudi Arabia , their applications, and how they contribute to the power transmission system design . Why Transmission Towers Are Crucial in Power Grid Development Every kilometer of transmission line construction requires careful planning. The right tower design ensures: Stable support for 69k...

ENGINEERING ARTICLES

Search This Blog