Electrical Panels of Cold Storage

Cold storages, like any industrial complex, require electrical power. The distribution, control, and optimization of electricity consumption in the industry are of great importance. Cold storages are no exception to this. In a cold storage, after the incoming power transformer, we deal with low voltage electricity, which has an approximate voltage of 400 volts and a frequency of 50 hertz in Iran. In a cold storage, we typically handle at least two categories of electrical panels: one for distribution panels and the other for power and control panels of the cold storage equipment. This article aims to briefly introduce these two sections and the related equipment and items, types of cold storage electrical panels, power and control circuits, cold storage automation, and so on.

Distribution Panels:

In factories and industrial workshops, after the electrical substation, which is the point of entry for electricity into the complex, distribution panels are usually placed. The purpose of these panels is to distribute the low voltage electricity that enters the complex from the transformer among the various units present in the factory and to protect each section separately against overload, short circuit, and similar issues. In cold storages, the incoming electricity to the relevant cold storage panel is usually branched from an initial distribution panel. In this distribution panel, an automatic switch or a fuse is considered for the protection of the cold storage panel and the incoming power cable to it.

Capacitor Panel:

In an industrial factory that has inductive loads, such as cold storages, the capacitor bank has special importance alongside the electrical substation and the distribution panel. Since inductive loads generate reactive power, it is necessary to eliminate this undesirable and costly power by placing an appropriate number of capacitors in the circuit. The number and capacity of the capacitors and the steps of their entry into the circuit must be calculated at the time of designing the complex, and suitable tools should be used to control the increase and decrease in the number of capacitors.

Classification of Cold Storage Electrical Panels:

Before explaining the nature and operation of the power and control circuits of cold storages, it is necessary to consider a general classification. Cold storages vary in size, type of refrigerant, type of compressor, method of sending refrigerant to the cold storage rooms, and other factors. To stay on topic, we will loosely classify cold storage panels into three sections:

Direct Freon System

Rack Freon System

Pumped Ammonia System

We will only explain two types of electrical panels: the direct freon system and the pumped ammonia system. It should be emphasized again that the conceivable types of cold storages exceed these three types, but due to the widespread application of these three categories, we have only mentioned them.

Electrical Panels of Pumped Ammonia Systems:

The electrical panels of ammonia cold storages are often complex and large. Given that the ammonia compressors currently in use generally have a larger input power than conventional freon compressors and that there are more cold storage units in ammonia systems, the total electrical power of these electrical panels is high. Consequently, the power circuits of these panels have larger protective switches and copper busbars compared to the electrical panels of freon systems. Typically, in design, the electrical panels of ammonia systems are considered as upright cells. The control circuits of these panels are also much more complex than those of freon panels. In the typical structure of an ammonia cold storage electrical panel, pressures, liquid levels, and temperatures from several points of the cooling process are measured, analyzed, and controlled. Among these points are the discharge pressure of the compressors, tank pressures, room temperatures, tank levels, and so on. With the advancements in technology, the electrical panels of ammonia cold storages have been directed towards utilizing new knowledge and employing industrial automation. More details about industrial automation and other new features will follow under the appropriate title.

Electrical Panels of Freon Systems

The electrical panels of freon cold storages usually have simpler circuits and smaller dimensions compared to other cold storage electrical panels. Typically, the power circuit of these panels includes the startup of three main cold storage equipment units, namely the compressor, condenser, and evaporator. The control circuits also manage the temperature of the cold storage and the pressures of the compressors. In the thermostat-controlled model, the possibility of manually starting the equipment via switches on the electrical panel door and automatic startup via a digital thermostat is provided. In the PLC-controlled model, both manual and automatic modes are available through a touch panel device.

Power Circuit:

The power circuit of the electrical panel includes three-phase and single-phase circuits used to start equipment such as electric motors and heaters. These circuits must have appropriate protection both at the input and output of each section. Typically, to protect electric motors, equipment such as thermal switches, bimetallic switches, and fuses are used, and for heater protection, miniature switches and residual current devices. Each of these devices provides one or more protections, such as overload protection, short circuit protection, protection against electric shock, and so on. In cold storage electrical panels, various methods are used to start electric motors. Depending on the type and size of the load, an electric motor can be started directly and instantaneously, in two steps, softly using a soft starter, or by changing the frequency smoothly and with speed control. Karmaye Sabz Kian Company utilizes all of these methods in its electrical panels based on the case and customer needs.

Control Circuit:

The control circuit in electrical panels is used to control the electrical panel equipment and subsequently control the related electrical devices. The control circuits of cold storage electrical panels usually include one or two levels of single-phase voltage of 220 Vac and 24 VDC. The activation of the contactors related to each load at the required and desired time, protection of equipment against pressure increase or liquid level in tanks, control of room temperature, and similar tasks are all made possible with control circuits. In older systems, control was performed using analog or digital local controllers along with switches and signal lights. In relatively new projects, thanks to the utilization of new technological advancements, instead of using all these diverse, scattered, and bulky devices, PLCs can be used. PLCs are programmable logic controllers that centrally control the entire cooling process in the cold storage electrical panel and provide extensive and efficient monitoring capabilities. Karmaye Sabz Kian Company has implemented numerous projects using both methods of controlling the refrigeration process, depending on customer choice.

Industrial Automation

Industrial automation, which has also been mentioned in the discussion of the control circuits of the electrical panel, has a wide range. However, in cold storage projects, it usually does not exceed two or three general categories. What has been common in cold storage electrical panels so far is the use of microcontrollers and PLCs, with PLC projects being divided into simple PLCs (Logo) and advanced PLCs. Here, for the sake of brevity, we will only address advanced PLCs. It is worth mentioning that this naming is chosen solely for convenience and efficiency in the cold storage electrical panel. The term PLC stands for Programmable Logic Controllers. In the control circuits of the cold storage electrical panel, PLCs can be used to eliminate complex wiring and the switches and lights on the panel door, as well as timers and scattered mechanical and digital controllers. Reading and processing the output of all sensors and measuring and control devices are done in the PLC. Monitoring and recording data and plotting graphs of their changes are greatly facilitated by industrial automation, providing new capabilities for the user. With industrial automation, remote connection to the control system via mobile, tablet, or computer, whether through internal networks such as Ethernet or via the internet, has been made possible.

Compressor Capacity Control Panel

The range of types of cold storage compressors is very wide, and we have been able to design our capacity control panels in such a way that they can be compatible with various types of cold storage compressors. Therefore, these capacity control panels can control piston freon compressors with capacity increase and decrease valves, screw freon compressors, piston or scroll freon compressors, or screw compressors that are arranged in parallel as a rack, as well as piston ammonia compressors and screw ammonia compressors, ensuring necessary protection against undesirable pressure and temperature increases and decreases in the control process.

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