11. A 25HP slip ring speed induction motor is to be used for driving a printing machine at Habari newspaper factory. The motor should provide the following; - forward and reverse speed rotations, - Three steps starting sequence, - coloured indicator for each major operation, Propose the right type of motor starter to be used and hence draw the well labelled main circuit \& control circuit diagrams which will fulfil the above requirements.

**Motor Starter Type** For a 25 HP slip ring induction motor that requires forward/reverse rotation with a three‐step starting sequence and status indication, the recommended starter is a **multi‐step (low voltage/resistor) reversing starter**. This starter is designed especially for slip ring motors and accomplishes: - **Forward and Reverse Rotation:** By using two separate contactor circuits (one for forward and one for reverse) with proper interlocking to prevent simultaneous energization. - **Three-Step Starting Sequence:** By inserting a resistor bank into the rotor circuit in three progressive steps. In the first step, maximum resistance is inserted to limit the inrush current. In the subsequent steps the resistance is reduced gradually until the motor is directly connected (full voltage) to the supply. - **Colour Indicators:** These are provided via auxiliary indicator circuits in the control circuit. For example, green may indicate “run”, red for “reverse” operation, and yellow for “starting” (when resistor banks are in circuit). Below are the well‐labelled diagrams for the main motor circuit and the control circuit. --- **Main Circuit Diagram** \[ \begin{array}{rcl} \textbf{Line Supply (L1, L2, L3)} & \rightarrow & \text{Main Circuit Breaker / Overload Relay} \\ & \rightarrow & \begin{array}{l} \textbf{Contactor / Starter for Forward Rotation (K\_F)} \\ \text{-- Motor winding connections arranged for forward rotation} \end{array} \\ & + & \begin{array}{l} \textbf{Contactor / Starter for Reverse Rotation (K\_R)} \\ \text{-- Motor winding connections reversed for reverse rotation} \end{array} \\ & & \\ \textbf{Resistor Bank} & \rightarrow & \text{Three resistor sections } (R1, R2, R3) \text{ connected in series with the rotor circuit (via slip rings).} \\ & & \text{The resistor bank is progressively cut-out using auxiliary contactors (CR1, CR2) as follows:} \\ & & \quad \text{Step 1: Full resistance (R1 + R2 + R3)} \\ & & \quad \text{Step 2: Partial resistance (R2 + R3)} \\ & & \quad \text{Step 3: Minimal resistance (R3 only) followed by direct online connection} \end{array} \] The motor rotor circuit is connected as follows: - The rotor (through the slip rings) is connected to the resistor bank assembly. - At the end of the resistor bank, contactors (or cut-out contacts) bypass successive resistor sections. - Finally, after the last step, the rotor is connected directly to the supply (direct online run). A simplified block diagram representation is: ``` L1, L2, L3 │ ┌────────┴────────┐ │ Main Circuit Breaker/OLR │ └────────┬────────┘ │ ┌─────────┴─────────┐ │ │ Forward Contactor Reverse Contactor │ │ └─────┬─────┬──────┬─┘ │ │ │ │ (Change motor winding connections) │ │ └─── Motor Armature │ ┌─────────┴─────────┐ │ Rotor slip rings │ └─────────┬─────────┘ │ Resistor Bank (R1,R2,R3) │ (Resistor cut-out contactors CR1, CR2 in sequence) │ Neutral or Return ``` --- **Control Circuit Diagram** The control circuit manages the starting process (three steps) and the forward/reverse selection. It includes: - **Start and Stop Pushbuttons:** A start pushbutton initiates the starting sequence; a stop pushbutton interrupts the circuit. - **Forward/Reverse Selection Switch:** A selector switch that energizes either the forward coil \( K_F \) or the reverse coil \( K_R \) with proper interlocking so that only one is active at a time. - **Timer Relay:** This controls the time intervals for the resistor cut-out sequence. The timer relay contacts (T1, T2, etc.) operate the auxiliary contactors which bypass resistor sections in steps. - **Indicator Lamps:** Colored lamps (e.g., green for running forward, red for reverse, yellow for starting) are connected to indicate the major operation stages. They are energized by auxiliary contacts on the main contactors and the timer relay. - **Interlocking Contacts:** Prevent simultaneous energization of forward and reverse circuits. A simplified control circuit schematic is as follows: ``` L1 Control Supply │ ┌──┴──┐ │ Stop│ (Normally Closed) └──┬──┘ │ ┌───┴────┐ │ Start │ (Normally Open pushbutton) └───┬────┘ │ ├─────────────┐ │ │ Forward Selector Reverse Selector (Forward coil control of K_F) │ │ └─────┬───────┘ (Interlocked so that once one is active, the other is blocked) │ [Timer Relay Unit] (T1 controls first resistor bypass, T2 controls second resistor bypass) │ ┌───────────┴────────────┐ │ │ Auxiliary Contacts Auxiliary Contacts for Resistor for Resistor cut-out bypass CR1 cut-out CR2 │ │ └────────┬───────────────┘ │ Indicator Lamps: ┌──────────────┐ ┌──────────────┐ ┌──────────────┐ │ Yellow (Start)│ │ Green (Forward)│ │ Red (Reverse) │ └──────────────┘ └──────────────┘ └──────────────┘ │ │ (Lamp circuits connected to respective auxiliary contacts) ``` **Operation Sequence** 1. **Starting:** When the start button is pressed after selecting forward or reverse, the control circuit energizes the selected motor contactor (\( K_F \) or \( K_R \)). Simultaneously, the timer relay is activated controlling the multi-step starting sequence. Initially, the resistor bank is fully inserted; the yellow indicator lamp lights up indicating starting. 2. **Step Changes:** After a preset time interval (controlled by T1), the first resistor (R1) is bypassed. A second interval (T2) then bypasses R2, leaving a minimal resistor (R3). When the motor reaches near full speed, R3 is also bypassed for full voltage operation, and the corresponding indicator (green for forward or red for reverse) is energized. 3. **Reverse Operation:** For reverse operation, the reverse selector ensures that the motor terminals are reconfigured accordingly. The starting sequence proceeds similarly, with the red indicator being activated once full speed is achieved. These diagrams and description meet the requirements for forward/reverse rotation, a three-step starting sequence (with intermediate reduced voltage operation achieved by stepped resistor cut-outs), and operational status indication using colored lamps.