Principles followed in the design of electrical control equipment

The general principles for the selection of electrical equipment are mainly as follows:

1) Select electrical equipment according to the working environment and normal working conditions.

1) Select the model of electrical equipment according to the location of the equipment (indoor or outdoor), the use environment and working conditions.

2) Select the rated voltage of the electrical equipment according to the working voltage.

3) Select the rated current of the electrical equipment according to the maximum load current.

The rated current of the electrical equipment in should not be less than the maximum load current imax (or calculated current ij) that actually passes through it, ie.

in≥imax

or in ij (7—1).

2) Verify the dynamic and thermal stability of electrical equipment according to the short-circuit condition.

In order to ensure that the electrical equipment will not be damaged in the event of a short-circuit fault, the dynamic and thermal stability of the electrical equipment shall be verified according to the maximum possible short-circuit current. Dynamic stability: The electrical equipment will not be damaged under the electrodynamic action generated by the impact short-circuit current.

Thermal stability: The heating temperature of the current-carrying conductor of electrical equipment does not exceed the allowable heating temperature of the current-carrying conductor for a short time under the action of the maximum hidden short-circuit tun current.

3) Verification of the cut-off ability of the switching appliance.

Electrical equipment such as circuit breakers and fuses are responsible for the task of reliably cutting off the short-circuit current, so the switching appliance must also verify the current breaking capacity, and the current breaking capacity of the switchgear is not less than the maximum three-phase short-circuit capacity of the installation site.

All kinds of electrical equipment and current-carrying conductors, due to their different uses and working conditions, so each type of electrical equipment and current-carrying conductors have specific selection conditions. However, regardless of the electrical equipment and current-carrying conductors, the basic requirements for them are the same, that is, they must work reliably in normal operation and short circuits. For this reason, there are general conditions for the selection of various electrical equipment, that is, the selection is carried out according to the normal working conditions, and its dynamic stability and thermal stability are verified according to the short-circuit state.

1.Select according to the rated voltage of normal operation.

The maximum allowable operating voltage of the selected electrical equipment and cables shall not be lower than the maximum operating voltage of the installed circuit. The maximum allowable working voltage of general electrical equipment and cables: when the rated voltage is 220kV and below, it is; When the rated voltage is 330 500kV, it is UE.

However, the maximum operating voltage of the actual power grid is generally not more than a time of the rated voltage UEW of the power grid. Therefore, in general, it can be selected according to the condition that the rated voltage UE of electrical equipment and cables is not lower than the rated voltage UEW of the power grid at the installation site.

2.Select according to the rated current of normal operation.

The rated current IE of the selected electrical equipment or the long-term allowable current of the current-carrying conductor IY shall not be less than the maximum continuous working current Imax of the installed circuit, that is, the conditions, IE (or IY) Imax shall be satisfied.

When calculating the maximum continuous working current of the circuit, the continuous working current of the circuit under various operating modes should be considered, and the maximum should be selected, such as the output of the generator and transformer remains unchanged when the voltage decreases by 5%, so the imax of the circuit = ;; The bus tie circuit breaker circuit can generally take the Imax of the largest generator or transformer on the bus; The maximum current of the bus segmented reactor should be the current required to ensure the load of the bus section when the largest generator on the bus trips, usually 50% to 80% of the rated current of the largest generator; In addition to considering the normal load of the line and the loss of the line, the maximum current of the outgoing circuit should also consider the load transferred from other circuits in the event of an accident.

For circuit breakers, disconnectors, reactors, etc., because there is no continuous overload capacity, under the condition that the maximum allowable heating temperature of each part of them does not exceed the specified value, when these equipment are used when the ambient temperature is higher than +40, but not higher than +60, the ambient temperature increases by 1, the rated current is reduced, and when the ambient temperature is lower than +40, the ambient temperature is lower by 1, the rated current is increased, but its maximum overload shall not exceed 20% of the rated current.

First, the basic principles of electrical equipment selection 1, according to the normal working conditions of the selection of electrical equipment 1, the selection of electrical equipment type of electrical equipment must consider the equipment location and working environment. In addition, according to the requirements of construction and installation, or the requirements of operation and operation, or the requirements of maintenance and overhaul, there are various different types of electrical equipment to choose from. 2. When selecting the voltage of electrical equipment, the rated voltage of the selected electrical equipment should be greater than or equal to the maximum working voltage that may occur under normal conditions, namely:

UN uet3, the selection of the rated current of electrical equipment The rated current of electrical equipment should be greater than or equal to the maximum load current during normal operation, that is, in IET China's current production of electrical equipment, the designer takes the ambient air temperature of 40 as the calculated value, if the ambient air temperature of the device site is lower than 40, every 1 low, the allowable working current of electrical equipment (such as circuit breakers, load switches, isolation switches, current transformers, and bushing insulators, etc.) can be increased than the rated value, However, the total increase cannot exceed 20%. 2. Verify electrical equipment according to short-circuit conditions 1, thermal stability verification of electrical equipment Thermal stability verification of electrical equipment is based on the value of short-circuit current of electrical equipment, and the following formula is often used in engineering to do thermal stability verification, that is, i2TT i2 tj or i it t tj formula IT—— Manufactured into the specified thermal stability current of electrical equipment within t seconds, this current is not to heat all parts of the electrical appliance to more than the specified within the specified time.

A few celebrities upstairs said a lot, and it all made sense, that is, there was more text. To put it simply, it is ten words in five aspects: safety, suitability, quality, economy, and margin.

Suitable is to meet the requirements of the use and environmental requirements, and the margin is to consider a certain margin, leaving a certain margin for further expansion or other factors in the future. I won't explain the rest.

Electrical control circuit copy

The basic principles that should be followed in the design are:

du(1) should meet the control requirements and protection requirements of mechanical equipment for electrical and gas control circuits to the greatest extent.

2) On the premise of meeting the requirements of the production process, we should strive to make the control line simple, economical and reasonable.

3) Ensure the safety and reliability of the control.

4) Easy to operate and maintain.

Principles of electrical control design:

1) To meet the requirements of electrical control of production machinery and production process to the greatest extent.

2) On the premise of meeting the requirements, make the control system simple, economical, reasonable, easy to operate, convenient to maintain, safe and reliable.

3) The selection of electrical components is reasonable and correct, so that the system can work normally.

4) In order to adapt to the improvement of the process, the equipment capacity should be left with margin.

Maximize the production of bai.

DUMomy and production process requirements for electrical control; Under the premise of meeting the control requirements, the design scheme should be simple, economical and practical; Properly handle the relationship between mechanical and electrical; Correct and reasonable selection of electrical components, reduce production costs, and ensure safe and reliable use; It is easy to operate and maintain, and the appearance is coordinated and beautiful.

1. To meet the requirements of production machinery and process for electrical control to the greatest extent. The requirements of production machinery and technology for the electrical control system are the basis of electrical design, and these requirements are often provided in the form of working cycle diagrams, execution of the original action beat table, detection element status table, etc., and for the occasion with speed regulation requirements, the speed regulation technical indicators should also be given. Other requirements such as starting, steering, braking, lighting, protection, etc., should be fully considered according to production needs.

2. Under the premise of meeting the control requirements, the design scheme should be simple and economical.

3. Properly handle the relationship between machinery and electricity. Many production machinery is the use of electromechanical combination control to achieve control requirements, from the process requirements, manufacturing costs, structural complexity, easy use and maintenance and other aspects of the relationship between the two.

4. Correct and reasonable selection of electrical components.

5. Ensure safe and reliable use.

6. Beautiful manufacturing, easy to use and maintain.