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Analysis of technical problems of dual power products

By:Nader Updated:August 18,2022 15:09PM

The analysis of technical problems of dual power products introduces the application scenarios, product classification, development history, characteristics and selection principles of dual power products.

01. Definition of dual power transfer switch

Transfer switch

Transfer switching equipment (TSE) is an electrical appliance composed of one or more switching devices, which is used to disconnect the load circuit from one power supply and connect it to another power supply. It is mainly used for the conversion between two power supplies, and can also be used for the conversion between loads.

Automatic transfer switch

Automatic transfer switching equipment (ATSE) is an automatic transfer switching device, usually including all necessary equipment for monitoring and switching operation. ATSE can have optional manual operation characteristics. According to the requirements of gb51348-2019 standard for electrical design of civil buildings (replacing the original jgj16-2008 and implemented on August 1, 2020).

02. Application scenario

Main application industries: real estate, industrial and commercial construction, information communication and industrial construction.

The use scenarios include: fire protection, fire emergency, passenger elevator power, sewage, security, normally open lighting, data center, urban comprehensive pipe gallery, etc.

03. Classification of dual power supply

It is divided into PC level, CB level and CC level according to short-circuit capacity:
1. PC: TSE capable of connecting and carrying, but not used for breaking short-circuit current;
2. CB: TSE equipped with overcurrent release, capable of connecting and carrying, and used to break short-circuit current; <r> 3. CC: TSE capable of connecting and carrying, but not used for breaking short-circuit current. The main part of the TSE is composed of electromechanical contactors meeting GB 14048.4

Main difference: the difference between PC level and CB level is whether it has the ability to break short-circuit current, and the switching speed of PC level is faster than that of CB level; The executive switch of CC level main body is a contactor, which belongs to special PC level.

According to the product structure, it is divided into special type and derived type
1. Special type: the main part of the electrical equipment is specially designed according to the requirements of 14048.11. It is an integrated TSE for power conversion, such as single pole double position and double pole double position
2. Derivative type: the main part of TSE shall be composed of electrical appliances with isolation function, and CB level products basically belong to derivative type

According to the product function, it is divided into bypass type, instantaneous parallel type and delay conversion type
1. Bypass type: TSE composed of mtse and ATSE. The mtse and the ATSE are connected in parallel in the circuit. When the ATSE exits the circuit, the manual mtse can complete the conversion between the two power supplies, which is mainly used in commerce, banks, airports and data centers
2. Instantaneous parallel type: TSE that can instantaneously connect two power supplies in parallel under specific conditions (such as voltage, same frequency and same phase angle) so that the load can be continuously converted, such as our products ndq5 and ndq5w
3. Delay conversion type: TSE with transient dwell time, which can be set according to the load nature of the connection

According to the control mode: manual operation, remote control operation and automatic conversion

Classification of subdivision control mode:
1. Connection mode of controller: integral type and split type
2. Controller control mode: automatic switching and automatic recovery, automatic switching and manual recovery and mutual standby

Total action time: from millisecond level to 15 level

04. Development history

The development of TSE can be seen as: CC level → CB level → PC level. The early dual power supply products were realized by the overlapping of contactors, which easily caused short circuit, contact adhesion and other faults. With the development and maturity of the circuit breaker, a dual power supply product with the circuit breaker as the executive switch has emerged, which is the CB level product. The development of PC level has gone through two stages. The first stage is to form a dual power supply product by using two disconnectors as actuators. The advantages are good short-term endurance and the disadvantages are weak breaking capacity and electrical life. In the second stage, the dual power supply technology of Japan and the United States will be introduced to design contacts suitable for the requirements of 14048.11, such as single pole double set and double pole double set contacts. The future development direction is miniaturization and intellectualization.

05. Characteristics and selection principles

Main characteristics

Electrical type, type of use, number of poles, working position, rated value and limit value of main circuit

Select according to the form of electrical appliance

1. Emergency power supply system: emergency power supply involves personal and property safety, so the power supply system of safety facilities should automatically supply power. PC level ATSE shall be selected, such as fire power supply system, and the switching time is required to be 0.1s ~ 0.25s.

2. Standby power supply system: for non safety facilities, the duration of power failure will not cause secondary disasters. Automatic power supply or non automatic power supply can be adopted. For example, if ATSE or mtse is selected, CB level ATSE can be selected, and the switching time is required to be 1s ~ 600s.

According to general principles:

  • 1. TSE rated value: the rated working voltage and frequency shall be consistent with the rated working voltage and rated frequency of the two power supplies; The rated working current shall not be less than 1.15 times of the rated current of the circuit
  • 2. Total action time:
    • (1) The total action time of ATSE should be compatible with the maximum allowable power-off time of load;
    • (2) In the low-voltage distribution system, the use of ATSE should not exceed level 3, and there should be time cooperation between the upper and lower levels;
    • (3) In the distribution system with bus tie switch, the delay of ATSE shall match with the switching delay of bus tie switch;
    • (4) The return transition time (TR) of ATSE shall be returned after a period of time after the common power supply is restored to the stable state;

Contact switching time: measure the time from the first group of main contacts disconnecting the common power supply to the second group of contacts closing to the standby power supply;

Switching action time: measure the time from when the deviation of the main power supply is detected to when the standby power supply is closed.

3. Contact temperature rise: pay attention to the problem that the contact temperature rise may be too high due to the oxidation of the contact of the switch apparatus at the standby power supply side due to long-term disconnection.

Select by limit value:

Rated short-time withstand current: the short-time withstand current value that can be carried by the electrical appliance under the specified test conditions specified by the manufacturer.

Rated limited short-circuit current: it is the expected short-circuit current value that the TSE protected by the designated short-circuit protection device (SCPD) can withstand within the action time of the short-circuit protection device under the specified test conditions specified by the manufacturer.

Select by use category:

The use category of TSE is related to the expected use conditions and is determined by the nature of the load. The use category determines the parameters to be tested at the time of certification, such as the ability to verify on and off.

Select by number of poles:

In TN-C system, three pole TSE shall be selected; To determine the number of poles of dual power supply, the most essential thing is to determine whether the neutral line needs to be disconnected. It is related to factors such as the type and setting mode of grounding system.

Select by working position:

Three section ATS should be selected at the power supply level or power distribution level. Two stage ATS can be selected for fire-fighting loads such as fire pump, fire elevator, smoke exhaust fan and emergency lighting.

06. Working principle

It is composed of a controller part and a mechanism part. The standby power supply is connected to the mechanism through the main circuit. The mechanism transmits the power supply to the controller through the sampling line, and the controller transmits the power supply to the sampling circuit and the power supply circuit. The power supply circuit will supply power through two-way phase voltages, and at the same time, the AC power will be converted into DC power, which will supply power to other modules.

For example, when the sampling circuit detects a phase failure, the single-chip microcomputer circuit judges that it needs to be switched. The drive circuit leads the power of the main circuit to the power source, so that the coil or motor can be powered on, driving the interlocking or transmission mechanism, so as to realize the switch or contact action. The common power supply is switched to the standby power supply, the common closing signal disappears, and the standby closing signal appears, which will be fed back to the position judgment circuit. The single-chip microcomputer circuit judges that the switching is successful, The drive circuit is driven to disconnect power from the power source.

07. Common fault handling

  • 1. Environmental inspection, key points: eliminate water and foreign matters;
  • 2. Fuse inspection;
  • 3. Key points of main circuit wiring: whether the connection is reversed or the n-line is not connected;
  • 4. Secondary circuit wiring, key points: active or passive;
  • 5. Other connection inspection, key points: mechanism and controller connection;
  • 6. Explicit setting of controller, key points: automatic / manual, delay time;
  • 7. Hidden setting of the controller, key points: working mode, voltage threshold and others;
  • 8. Manual operation, key points: find fault points through handle or key operation;
  • 9. Other inspection, key points: CB level product switch tripping, communication address setting, etc;