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Temperature rise test
What is temperature rise test
Temperature rise test is a routine test item in the type test of
electrical products. The purpose of temperature rise test is to
test the temperature change of electrical products and components
to determine whether the electrical products or components meet the
requirements of the standards. With the rapid development of
electrical products, temperature rise test has become more and more
important for the safety of electrical equipment and components.
Temperature rise test is a type test item and one of the main test
items for new product finalization. For derivative products or
normal products, due to major changes in product technology,
substitution of raw materials for major components, and actual loss
values in factory products exceeding the standard, when it is
doubted whether the rated power can be reached, temperature rise
test shall be carried out. Temperature rise test is for the safety
performance test of electrical connection equipment such as power
cord connectors, sockets, extension boards, conversion plugs,
wiring terminals, connectors, switches, etc.
Temperature rise test standard
Temperature rise test has clear requirements in safety standards
for electronic and electrical products such as GB8898 (IEC60065),
GB4943 (IEC60950), GB4706 (IEC60335), and GB7000 (IEC60598). Its
test methods mainly include thermocouple method and resistance
method.
Thermocouple method is to paste thermocouples on the surface of equipment parts and calculate the temperature rise by measuring the temperature of the surface of equipment parts with temperature measuring instruments. When measuring the influencing factors of temperature rise by thermocouple method, the influence of factors such as thermocouple, temperature measuring instrument, adhesive, test environment conditions, and test engineer's operating level should be considered in advance, and these influencing factors should be controlled to a minimum.
Purpose of temperature rise test
To judge the storage or working adaptability of products under
temperature change conditions. The purpose of the identification
test is to check whether the product meets the requirements of the
relevant standards; the improvement test is mainly used to evaluate
the durability and reliability adaptability of the product under
temperature change conditions.
Temperature rise test conditions and procedures
Test conditions
Voltage: the upper and lower limits of the rated voltage or the upper and lower limits of the rated voltage range
Frequency: the upper and lower limits of the rated frequency or the
upper and lower limits of the rated frequency range
Load: the heavy load during normal operation or the severe
situation in the load combination (the case of large input
current).
Environment: If UL certification is required, the test can be
carried out at room temperature. If TUV certification is required,
the test must be carried out at a high working temperature.
Note: If this test is carried out at room temperature, the
conversion problem must be considered: the measured temperature
plus the difference between the high working environment
temperature and the room temperature is the final temperature.
Thermocouple position:
All key components. If in the same or similar position, one of them
can be taken.
Note: For key components, please refer to Chapter 2 "Safety
Components" of this document.
Test process
1. Determine the components to be tested.
2. Glue the thermocouple to the components to be tested. Pay
attention to the location of the thermocouple, which should be a
place where the heat may be serious.
3. Turn on the machine, adjust the input voltage to the upper limit
of the rated voltage or the upper limit of the rated voltage range,
adjust the input frequency to the lower limit of the rated
frequency or the lower limit of the rated frequency range, and
adjust the output load to the required size.
4. Let the test equipment continue to work until the test equipment
reaches thermal equilibrium.
5. Record the reading of the thermocouple.
Note: If the change of the thermocouple reading within 30 minutes
is less than 1°C, it can be considered that the thermocouple has
reached thermal equilibrium.
Temperature rise test example
Motor temperature rise test
The rated temperature rise of the motor refers to the maximum
allowable temperature rise of the motor winding at the specified
ambient temperature (+40°C) in the design, which depends on the
insulation level of the winding. The temperature rise depends on
the heating and heat dissipation of the motor during operation. The
temperature rise is often used to judge whether the heat
dissipation of the motor is normal. The motor temperature refers to
the actual heating temperature of each part of the motor. It has a
great impact on the insulation material of the motor. Excessive
temperature will cause insulation aging, shorten the life of the
motor, and even cause insulation damage. In order to prevent
insulation aging and damage, the temperature of various parts such
as the motor winding is restricted from time to time. This
temperature limit is the allowable temperature of the motor.
Terminal temperature rise test
1. GB/T 14048.7, IEC 60947-7-1 standards: Install 5 terminal blocks
horizontally on the guide rail and connect them in series through a
1m long wire with a rated cross-sectional area. Load the test
current required by the rated cross-sectional wire upward and
record the temperature rise data of the middle terminal. When the
temperature is 20℃, the maximum allowable temperature rise of the
terminal block is 45K. Then the terminal block is tested for
voltage drop.
2. GB/T13140, IEC60998, UL1059 standards: The test process is
essentially the same as above, the only difference is the length of
the wire. If ≤16AWG, the length is 18 inches (0.46m); if ≥14AWG,
the length is 48 inches (1.22 m). Install the three terminals
horizontally adjacent to each other. The ambient temperature during
measurement is 25°C, the maximum allowable temperature rise is 30K,
and the measurement is as close to the wiring position as possible.
Temperature rise test judgment
The temperature measured by the component should be within its
rated high operating temperature.
Temperature limit: Below are the temperature limits of some
materials
Temperature rise requirements for insulating materials: (Insulating
materials include: all parts of transformers, etc., but excluding
thermoplastic materials)
Maximum temperature during normal operation Maximum temperature
during abnormal operation
Class A materials 100℃ 150℃
Class E materials 115℃ 165℃
Class B materials 120℃ 175℃
Class F materials 140℃ 190℃
Class H materials 175℃ 210℃
If the temperature rise of the winding is measured by thermocouples, the above temperature limits should be reduced by 10℃. In addition, each certification agency may have some additional requirements, such as additional margin requirements, etc.
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