Design of a Power Panel for a water cooler

This was posted on 2013-04-14

Certain machines uses closed circuit continuous circulating water to cool the temperature of the produced goods. This water is in turn cooled by the cooling system. The temperature of cooling water varies depending on the number of extrusion machines switched on and the type of wires used by these machines. Therefore the requirement for cooling only exists when the temperature of the cooling water exceeds a predetermined level. However the cooling tower at the factory works continuously due the lack of a system to detect the temperature of the water entering into it. A temperature sensitive system is needed to switch off the cooling tower fan when water temperature of the incoming water is lower than a set level. When the cooling tower keeps on working continuously, it results in an immense loss of energy. To rectify this problem the company has requested a power panel that works on a temperature feedback that control the cooling tower.

Water Cooler

The cooling system consists of three tanks, cooling tower and a circulating water pipe network. The input to the power panel is a K-type thermocouple placed on the inner wall of the pipe in which water flows from the reserve tank to the cooling tower. The thermocouple reads the temperature of the water entering the cooling tower. The input measures the temperature of the water and sends an analogue signal to a temperature controller. The designed cooling tower panel makes use of a Selec CH403 temperature controller. When the detected temperature from the input falls below a required level, this device automatically outputs a signal to the control system of the power panel.

The electrical system is connected to three phase power supply with neutral and earth. The output loads of the system were three pumps and a fan. The power ratings of each of these motors were obtained by reading the motor identification plate and also by manually operating the motors under their normal load, and measuring the current drawn by each motor read by a clamp current meter



Current Rating

Measured Current

Cooling Tower Fan Motor

415V L-L



Pump 1 Motor

415V L-L



Pump 2 Motor

415V L-L



Pump 3 Motor

415V L-L



A 3 pole circuit breaker rated at 30A was used as protection to the input three phase power supply. The output wires of the 3 pole circuit breaker was divided to parallel supply lines and given to four 3 pole motor protective circuit breakers and two single pole circuit breakers rated at 1A. One of the single pole circuit breakers was wired to an alarm system that signals if the total water level in the tanks has reduced and the Selec CH403 temperature controller. The other circuit breaker was wired to the control system in the power panel (Figure 1). The Selec Temperature controller was also connected to a K-type thermocouple fixed on the inner wall of the input water pipe to the cooling tower.

Water Cooler

All the motors are connected in the identical manner: The motor protective circuit breakers are in parallel in the power system. They provide the first line of protection for the motors connected to the system. The 3 phase wire from motor protective circuit breaker passes though the ‘normally open’ contactor points and connects to three end terminals which in turn supplies power to each motor.

Water Cooler

The CH403 Selec Temperature controller provided a relay output when the temperature detected was below the set value. The rated current of the relay points of the temperature controller was not sufficient to control the coil of the contactors used. As a result an external relay was used as an intermediate switch to handle the current needed by the contactor coil.

The first contactor which controls the cooling tower fan was wired directly from the overload of the motor protective circuit breaker to a selector switch and through the CH403 relay ‘normally open’ points. This allowed the temperature controller to control the temperature when the selector switch is switched to the ON position.

Water Cooler

The remaining motors contain contactors to operate the pumps of the cooling system. The control wire was initially wired to the overload of the motor protective circuit breakers and then through the ‘normally closed’ points of the stop button. The control wire then splits to create a parallel path for the start button and the contactor ‘normally open’ point to cause a self latch when the start button is pressed. The control wire is then connected to their respective contactor coils. However in the second pump (contactor 3), a ‘normally open’ point of the contactor 2 is added to make this pump dependent on the status of the first pump. The second can now only be switched on when the first pump is activated. The third pump works on the same principle as the first pump, thus both have no dependency on the status of any other pump.

Water Cooler

The lighting for the control system buttons was taken from their respective contactors. The green light for the on status was taken from the normal open points of the contactor while the red light from the off status was taken from the ‘normally closed’ point of the contactor. Where ‘normally open’ points were not available on the contactor, the green light was wired parallel to the coil of the contactor to give the same output.

The construction of the panel began by understanding the necessary safety requirements to operate different machinery and to handle components.

Initially the main components were laid on the panel base and their positions were optimised for the cleanest wiring. Cable Casings and the component rail for the circuit breakers, contactors and end terminals were drilled and fixed. Once the components were in place the electrical wiring for the system was connected. The cables were fixed according their phase colour code and with proper lugs on either side to provide better contact with the component

The circuit was completed by fixing the door. The door of the panel was measured and drilled to accompany the switches and lights. The space for the temperature controller was slowly cut out using a jigsaw (Figure 7). The control wiring for the switches lights and temperature controller was completed as described above (Figure 8). The wires were cleaned up using the cable ties and flexible cable holders

Water Cooler

Water Cooler

During a power outage at the factory, the machines are automatically shutdown. The time was made use of by fixing the power panel and connecting the power panel to the cooling system

Water Cooler

Water Cooler

Water Cooler

Water Cooler


When the power supply to panel was initiated the circuit breakers that were switched off prevent the flow of current. The circuit breakers switch on the power supply to all the components of the power panel.

The control system was switched on and all the switches on the panel door were tested. The control system for the 1st and the 3rd pump contactors was found to switch on independently whilst the 2nd pump contactor status was dependent on the status of the 1st pump contactor.

The Selec CH403 temperature controller was set to the temperature of 38 degrees Celsius manually. Then heating up the thermocouple to 38 degrees Celsius resulted in the switching on of relay output. Cooling the thermocouple to 37.8 degrees Celsius resulted in switching off the relay output, which in turn switched off the fan contactor. After subjecting the thermocouple to varying temperature ranges the temperature regulatory system was found to be working successfully.

When all circuit breakers and motor protective circuit breakers were switched on, the measured power supply that was received at the motors was found to be the rated value. Therefore motors were driven at their optimum speeds without causing problems in the components of the power panel.

Over a set period of time the temperature control system of the circulating water was observed for evaluation. During this period of time the cooled water temperature did not vary significantly. A graph depicting the temperature against time of the circulating water when the new and old power panel were used is shown below. The evaluation was conducted on different days where the extrusions machines were operating continuously for the standard duration of time.

Water Cooler

During the observed time of seven hours the cooling tower fan was found to be working for approximately three hours. Therefore, the new power panel implemented approximately saved energy as much as 43%.


The successful operation of the power panel require correct assembly of components for the optimal utilisation of power panel output in a manner to harvest
- A suitable feedback temperature regulation with fault warning alarms,
- Uninterrupted power supply to the outputs,
- High overall machine efficiency at a regulated temperature control,
- Minimum power utilisation,
- Minimal system drawbacks,
- Protection for the panel operator and for the components.

The power panel for the cooling system is controlled by a group of inputs that contain both manually operated switches and automatic signal generators. The manual switches give access to the panel operator to start and stop the main outputs of the cooling system. The automatic input contains a temperature detection device and a temperature regulator.

The temperature detection device used to measure the temperature of the water is a K-type thermocouple. This mid ranged industrial thermocouple contains Chromel and Alumel to measure temperature between -200 to +1350 degrees Celsius. The nickel constituent in the thermocouple changes its magnetic properties due to heat. This provides an analogue range of values that represents the temperature detected by the thermocouple.

Type E and type J thermocouples made of Chromel – Constantan and Iron – Constantan respectively have a smaller range and higher sensitivity that provides a better accuracy than the K-type thermocouple used by this system . However the company preferred to use the K-type thermocouple to simplify the use of thermocouples. The K-type thermocouples are used in all other machines at the factory.

The K-type thermocouple should be placed in a location where the temperature is read with direct water contact. Hence the thermocouple was fixed on the inner wall of the entry pipe to the cooling tower. This then encounters the water circulated through the extrusion machines and is entering the cooling process of the cooling tower. When the temperature of the water at this point is detected, the power panel and the cooling tower have sufficient time to react and regulate the temperature of the water.

The temperature control system used for this system is a Selec CH403 Temperature Controller. The controller performs the task of analysing the voltage reading that represents temperature. It reads the analogue signal from the K- type thermocouple and converts it to a temperature reading by means of its programmed algorithm. The temperature reading is displayed on the screen for reference. If the displayed reading is greater than the set value an internal relay is energised for external control purposes.

Selecting Selec CH403 Temperature controller is simpler and cheaper as opposed to designing a circuit to perform the same task. Other similar temperature control devices such as the Selec TC344 and TC544 Temperature Controllers, implements elaborate functions with closed loop controls such as Proportional Integral (PI) control to control the output. Conducting a research found out that the time taken to lower or raise the temperature of a large amount of water in the cooling tower is considerably high. Therefore a high precision closed loop control system would perform the same task as the Selec CH403. Thus it is not the best solution for the cooling tower.

The outputs of the power panel consist of four motors that control different aspects of the cooling system. One of the motors controls the fan of the cooling tower which lowers the temperature of the water entering the cooling system. The remaining three motors drive industrial centrifugal pumps for recirculation of water around the closed circuit cooling system.

The rated current for each motor was identified prior to selection of the necessary components and wires needed for the panel. Although the rated current on the identification plate of the motor was marked, it was not taken into account. The real current drawn whilst motor in normal operation proved to be more practical. This is because the current drawn at normal operation of the motor is the average current needed for the uninterrupted operation of the cooling tower. If the current value increases more than the current at normal operation, then it can be assumed that there is a fault in the cooling system. This can be assumed even if the current is less than the rated current value given on the motor identification panel.

The current value was calculated using a clamp current meter around the power wire for each motor. The suitable rated current for each motor was selected by adding 10% to the practical value to keep a safety margin.

The motors used at the Factory, for the cooling system had been functional for over 15 years. The motor windings, impellers and rotor are assumed to be worn out due to the regular use of the pumps over a long period of time. These pumps can be replaced with newer industrial centrifugal pumps that have a higher efficiency. However company did not replace the pumps and the cooling tower fan of the cooling system on this occasion.

The gauge of the wires needed for the electrical system was selected using the sum of the maximum selected current ratings of the motors. A safety margin was also added to the wires to ensure than the wires do not heat up at any point in the operation

A wire gauge of 7/0.67 (seven strands of copper where one strand has a diameter of 0.67mm) was sufficient for a current of 24A and length of two meters. This wire was used for the three phase system of the panel. A smaller flexible wire was used for the neutral wire as there is not much current in the neutral wire. This is because the coils motors are connected in the delta arrangement. The current flowing in the neutral wire includes only the current from the control circuit, lamps, harmonic noises and the current due to any reactive power in the inductive motor windings. The earth wire used was a 7/0.67 wire which is sufficient to allow any leakage current to be earthed before causing any harm to the panel components and panel operators.

A circuit breaker rated at 30A is suitable for this panel as it allows the maximum current needed by the pumps and any other current needed by the control system to pass through. However it is not expected of the circuit breaker to disconnect the circuit first, due to a fault in a motor. The motor protective circuit breaker values are set exactly to their recalculated safe rated current to immediately switch off when there is any instance where excess current is drawn. The single pole circuit breakers rated at 1A are safe to supply power to the control system.

The path to the motor from the motor protective circuit breaker is obstructed by a contactor on each line which allows the motors to be switched on an off using a control system. These contactors from Schneider were used instead of relays to allow a higher current to pass through the points without causing any resistances that may heat up damage the component. Each contactor was built with three pairs of ‘normally open’ points for the main power wires, a pair of ‘normally open’ points and pair of ‘normally closed’ points for the control system. The second contactor which powered the first pump was equipped with an auxiliary to add more control ‘normally open’ and ‘normally closed’ points.

The control system used for the panel controls all four motors. These motor protective circuit breakers from Schneider added an overload element which acts as a switch that shows the status of the Motor protective circuit breaker. The control system for each motor was passes through this overload so as to switch off the contactor when the motor protective circuit breaker switches off due to a failure in the motor. This prevents the current from flowing back the motor if the motor protective circuit breaker is energised accidently without fixing the fault. The start button has to energize again to continue the current flow to the motor.

The first and the second pumps in the cooling system were interlinked using the control system. This prevents the operator from switching on the second pump without switching on the first pump. If this system was not present, switching on the second pump only will cause the water in the extrusion machines to overflow to the factory flow.

The power panel and the cooling system at the factory do not represent a flawless model. There are some drawbacks to the system that do not have an impact as often as those rectified by this project. The neglected drawbacks that were identified are as follows.

1. A malfunctioning component in the power panel can be readily detected when the circuit is broken due to unnatural use of current. A malfunctioning thermocouple will not send the correct temperature reading to the temperature controller and this can mislead the power panel. Such a defect cannot be detected by the newly installed system. This will lead to overheating of produced wires leading to damaged goods that cannot be sold to the consumer. To rectify this problem a second temperature detector must be added record temperature at a different point in the cooling system and provide feedback to a visual or audible alarm system. Such a device may be installed to the collector basin of the cooling tower or the cooling bath of each extrusion machine to ensure the temperature of the water is at the correct level.

2. An obstructed flow in the pipe network will result in the stop of the continuous flow in the system. This will cause multiple problems in the system. The pumps of the cooling system will pump water against a large force causing the pump to draw a large amount of current and switch off the motor protective circuit breaker. The lack of cooling circulating water flow to the machinery will affect the quality to the wires manufactured. To rectify this problem a flow detection system is an essential requirement that need to be added to the power panel to monitor uninterrupted water flow and an alarm system to indicate an error in the flow system and the motor protective circuit breaker.

The cooling system consists of three tanks and the cooling tower. The three pumps are used to drive the water around the closed circuit through the factory machines and the tanks.

Water Cooler

The cooling tower used is a closed circuit dry cooling tower that relies on air to cool the liquid down to the desired temperature. The working principle of the cooling tower is called ‘counter flow’. In this design water is sprinkled through high pressure nozzles to a fill material. Air is drawn up in the opposite direction from an opening in the bottom to a fan fixed on the top of the cooling tower. This causes the cool air to absorb the temperature of the water.

Water Cooler

The power panel switches off the cooling tower fan when the temperature reaches a set value. This stops the water being further cooled by the cooling tower. The set value of the cooling tower is set to 34 degrees Celsius which is a value close to and higher than the temperature of the atmosphere. This prevents the water from heating up by the any environmental influences before reaching the extrusion machines. This helps to increase the energy efficiency of the entire system by preventing the loss of energy.

The counter flow system of the cooling tower could be improved further by creating a heat transfer system between the cool and the warm water pipes. The heated water and the cooled water pipes can pass side by side or inside each other to draw away from the heat from the warm water. In the process most of it is then radiated to the atmosphere. This allows the cooling tower to only remove the remaining extra heat from the returning water.

The counter flow system of the cooling tower could be improved further by creating a heat transfer system between the cool and the warm water pipes. The heated water and the cooled water pipes can pass side by side or inside each other to draw away from the heat from the warm water. In the process most of it is then radiated to the atmosphere. This allows the cooling tower to only remove the remaining extra heat from the returning water.

The extruder machines are not switched on all the time. Variable speed drives can be used to measure the demand of water needed by the factory and control the amount of water pumped. This reduces the energy used by both the pumps and the cooling tower fan. The pumps do not need to function at their maximum speed the entire time. Reducing the speed of the motor reduces the amount of energy used and also increases the efficiency of the pump. The cooling tower fan will be switched off more often as the temperature of the water to cool will be easier to reduce when there is less water flowing.

The cooling tower system uses a considerable amount of energy to operate continuously. Alternative energy sources that can be used for this system include
- solar power,
- wind power,
- kinetic energy of the water falling in the cooling tower,
- Kinetic energy of the water flowing due to gravity in the cooling pipe network.

The energy from these sources can be stored in an industrial battery and provide power for the cooling system when the price of electricity is at its peak time.

The system already implemented need to be further improved by adding the modifications described to increase the energy efficiency and a system of monitors to detect the malfunctions of the cooling system due to causes other than the thermocouple faults. The entire system when linked to the same power panel can be regarded an ideal model for the Kelani Cable Factory that operates water cooled wire extruding machines.


The panel performed well at controlling the outputs of the cooling tower. The temperature of the cooled water was maintained at a level close to the predetermined value. The panel also provided proper protection for both the users and the cooling system. The panel was organized and easy to troubleshoot. A clear increase in energy was seen when the pump is switched off when there is no need to further lower the temperature of water.

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