Indepth Electrical engineering

Why Induction Motors Are Not Kept Running in Star Connection Induction motors are sometimes started in Star connection (using a Star-Delta starter) but are always run in Delta for normal operation. The reasons are: 1. Voltage Reduction in Star In Star connection, V p h a s e = V l i n e 3 V_{phase} = \frac{V_{line}}{\sqrt{3}} This means each winding receives only 57.7% of the line voltage . 2. Current Reduction Since I p h a s e = I l i n e I_{phase} = I_{line} , the line current drawn is lower. Current is reduced in proportion to the reduced voltage. 3. Torque Reduction Motor torque is proportional to the square of the applied voltage : T ∝ V 2 T \propto V^2 So, in Star: T s t a r = ( 1 3 ) 2 × T d e l t a = 1 3 T d e l t a T_{star} = \left(\frac{1}{\sqrt{3}}\right)^2 \times T_{delta} = \frac{1}{3} T_{delta} This means the motor can produce only one-third of the rated torque . 4. Power Reduction Motor input power is proportional to voltage × ...

Star-Delta Starter: Working Principle, Circuit, and Applications Introduction For induction motors up to 7.5 kW , a Direct-On-Line (DOL) starter is commonly used. However, for motors above 7.5 kW , starting them directly causes large inrush currents that can disturb the supply voltage. To overcome this, industries widely use the Star-Delta Starter —a simple, reliable, and economical motor starting method. Working Principle of Star-Delta Starter The Star-Delta Starter reduces the motor’s starting current by initially connecting the stator windings in Star (Y) and later switching to Delta (Δ) after a preset time. 1. Star Connection (Wye) Phase current = Line current Phase voltage = Line voltage ÷ √3 Starting voltage reduced by 1/√3 (≈58%) Torque reduced to 1/3 , since torque ∝ V² Starting current reduced to 1/√3 of DOL current ✅ Advantage: Reduced inrush current. ❌ Limitation: Reduced starting torque. 2. Delta Connection (Δ) Phase voltage = Line voltag...

Earlier we discussed about Direct Online Starter Basic Circuit. For Basic Circuit diagram of Direct online visit at link below:- http://electrialstandards.blogspot.in/2014/04/direct-online-dol-starter.html Now let’s discuss about Direct online Starters following circuits:- 1 .        Reverse forward direct online Starter. 2.        Limit Switch & level Switch circuit in DOL. 3.        Remote Start/Stop Direct online Starter Circuit. Let’s discuss their  circuitry  one by one:- 1.       Reverse Forward Direct Online Starter:- Power and control circuit for Reverse forward Direct online starter is as below:- In control circuit C1 contactor is used as forward contactor and C2 contactor is used as Reverse contactor And also Reverse contactor NC is used in series with Forward contactor starting and also forward ...

Direct Online (DOL) Starter – Working, Circuit Diagram, Advantages & Disadvantages 🔹 What is a Direct Online (DOL) Starter? A Direct Online Starter (DOL Starter) is the simplest and most commonly used method to start induction motors. In this method, the motor is directly connected to the full line voltage. Because of this, it draws 6–8 times the rated current at startup. 👉 DOL starters are generally used for motors up to 7.5 kW (10 HP), where the inrush current can be tolerated by the electrical system. 🔹 Main Parts of a DOL Starter A basic DOL starter consists of the following components: Electromagnetic Contactor – Connects/disconnects supply to motor. Overload Relay (O/L Relay) – Protects the motor from overcurrent and overheating. Main MCB – Provides protection against short-circuits and faults. ON/OFF Push Buttons – Used to manually start and stop the motor. 🔹 Circuit Diagrams of DOL Starter 1. Power Circuit Diagram The Power Circuit ...

🔋 Battery Rating Calculation for UPS Systems 1. Why Series Connection? Series Connection → Voltage adds up, current remains same. Example: 18 batteries × 12V each → 216V DC bus. 2. Formula for Battery Capacity (AH) Battery Capacity (AH) = D C   C u r r e n t × D u r a t i o n   ( H r s ) %   C a p a c i t y   U t i l i z a t i o n \text{Battery Capacity (AH)} = \frac{DC\ Current \times Duration\ (Hrs)}{\%\ Capacity\ Utilization} Where: D C   C u r r e n t = U P S   ( K V A ) × 1000 × L o a d   P F η i n v e r t e r × E n d   V o l t a g e DC\ Current = \frac{UPS\ (KVA) \times 1000 \times Load\ PF}{\eta_{inverter} \times End\ Voltage} V A H = A H × V n o m i n a l VAH = AH \times V_{nominal} 3. Worked Example (UPS = 5 KVA, 1 Hr Backup, 18 Batteries) Step 1 – Find DC Current: D C   C u r r e n t = 5 × 1000 × 1 0.95 × ( 10.5 × 18 ) = 27.85   A DC\ Current = \frac{5 \times 1000 \times 1}{0.95 \times (10...

Maximum Allowable Temperatures of Various Types of Insulation in Motors Insulation materials play a crucial role in determining the efficiency, safety, and lifespan of electrical machines such as motors and transformers. The permissible operating temperature of an insulation system is defined by its Insulation Class , and exceeding this limit drastically reduces the machine’s service life. Insulation Classes and Maximum Temperatures Insulation Class Maximum Permissible Temperature (°C) Typical Materials Used Y 90 Cotton, silk, paper A 105 Cotton, silk, paper impregnated with varnish, oil, or enamel E 120 Modified synthetic materials B 130 Mica, asbestos, glass fiber with varnish or adhesives F 155 Improved Class B with epoxy resins, mica, silicone varnish H 18...

🔑 Circuit Breaker Life (Mechanical vs Electrical Operations) 1. Mechanical Life (No-load ON/OFF cycles): ·          Refers to how many times a breaker can be operated (ON/OFF) without current load. ·          Purely mechanical endurance, limited by moving parts, springs, and latching systems. 2. Electrical Life (Load/Short-circuit switching operations): ·          Refers to the number of ON/OFF or trip operations under load/current. ·          Limited by arc-quenching capability and contact wear . 📊 MCCB (Moulded Case Circuit Breaker) Life Expectancy MCCB Rated Current Mechanical Life (Ops) Electrical Life (Ops) ≤ 100 A 8,500 1,500 100 A – 315 A 7,000 1,000 315 A – 630 A ...