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# Transformer loss calculation method

Transformer loss calculation method
Transformer loss power is divided into iron loss and copper loss, iron loss, also known as no-load loss, is its fixed loss, the real is the loss generated by the iron core (also known as iron core loss, and copper loss is also called load loss).
One
Transformer loss formula
(1) active loss: ΔP = Po + KT β2 Pk
(2) reactive power loss: ΔQ = Qo + KT β2 Qk
(3) Comprehensive power loss: ΔPz = ΔP + KQΔQ
Qo ≈ Io%Sn, Qk ≈ Uk%Sn
Where: Qo – no-load reactive power loss (kvar)
Po – no-load loss (kW)
Pk – rated load loss (kW)
Sn–Transformer rated capacity (kVA)
Uk% – short-circuit voltage percentage
β–Load factor, the ratio of load current to rated current.
KT – load fluctuation loss coefficient
Qk – rated load leakage power (kvar)
KQ – reactive power economic equivalent (kW/kvar)
Selection conditions for each parameter in the above formula calculation:
(1) Take KT = 1.05;
(2) For urban power grid and industrial enterprise power grid 6kV ~ 10kV step-down transformer to take the minimum load of the system, its reactive power equivalent KQ = 0.1kW/kvar;
(3) Transformer average load factor, for agricultural transformers can be taken β = 20%; for industrial enterprises, the implementation of three-shift system, can be taken β = 75%;
(4) Transformer operating hours T = 8760h, maximum load loss hours: t = 5500h;
(5) transformer no-load loss Po, rated load loss Pk, Io%, Uk%, see the product factory information shown.
Two
Transformer loss characteristics
Po – no-load loss, mainly iron loss, including hysteresis loss and eddy current loss;
Hysteresis loss is proportional to the frequency; with the maximum flux density of hysteresis coefficient of the second power is proportional.
Eddy current loss is proportional to the product of frequency, maximum flux density, and thickness of silicon steel sheet.
Pc – load loss, mainly load current through the winding on the resistance of the loss, generally known as copper loss. Its size varies with the load current, and the load current is proportional to the square; (and with the standard coil temperature conversion value to express).
Load losses are also affected by the temperature of the transformer, while the leakage flux caused by the load current produces eddy current losses inside the winding and stray losses in the metal part outside the winding.
The total loss of the transformer ΔP = Po + Pc
Transformer loss ratio = Pc /Po
Efficiency of the transformer = Pz/(Pz+ΔP), expressed as a percentage; where Pz is the output power of the secondary side of the transformer.
Three
Calculation of transformer loss power
Transformer loss power has two parts: iron loss and copper loss. Iron loss is related to the running time, copper loss is related to the load size. Therefore, the loss of power should be calculated separately.
1, iron loss power calculation: different models and capacity of iron loss power, the formula is: iron loss power (kWh) = no-load loss (kW) × power supply time (hours)
Distribution transformer no-load loss (iron loss), checked by the attached table, the power supply time for the actual operation of the transformer time, determined in accordance with the following principles:
(1) For users of continuous power supply, the whole month is calculated as 720 hours.
(2) due to grid reasons intermittent power supply or power limit pulling road, according to the substation to the user the actual number of hours of power supply, shall not be difficult to calculate on the grounds that the full month of operation is still calculated according to the transformer blackout, since the fall of the fuse tube to the power supply station time, in the calculation of iron loss should be deducted.
(3) transformer low voltage side equipped with a cumulative clock users, according to the cumulative clock accumulated power supply time calculation.
2, the calculation of copper loss of electricity: when the load factor is 40% and below, according to the whole month of electricity consumption (to the meter readings) of 2% of the charge, the formula: copper loss of electricity (kWh) = monthly electricity consumption (kWh) × 2%
Because the copper loss is related to the size of load current (electricity), when the monthly average load ratio of distribution substation is more than 40%, the copper loss electricity shall be charged at 3% of monthly electricity consumption. The monthly electricity consumption when the load ratio is 40% is checked by the attached table. Load factor is calculated as follows: Load factor = copy of the electricity / S. T. Cos ¢
Where: S – the rated capacity of the distribution substation (kVA); T – the whole month calendar time, take 720 hours; COS ¢ – power factor, take 0.80.
Power transformer loss can be divided into copper loss and iron loss. Copper loss is generally 0.5 per cent. Iron loss is generally 5~7%. Transformation loss of dry-type transformer is smaller than that of oil-encroached type. Total transformation loss: 0.5+6=6.5 Calculation method: 1000KVA×6.5%=65KVA
65KVA × 24 hours × 365 days = 569,400KWT (degrees)
The labels on the transformer have specific data.
Four
Transformer no-load loss
No-load loss refers to the transformer secondary side of the open circuit, the primary side of the plus rate and the rated voltage sine wave voltage when the transformer draws power. Generally only pay attention to the rated frequency and rated voltage, sometimes on the tap voltage and voltage waveform, measurement system accuracy, test instruments and test equipment but do not pay attention to. Calculated value of the loss, standard value, measured value, the guaranteed value and confused.
If the voltage is added to the primary side, and there is a tap, such as the transformer is constant flux regulation, the added voltage should be the corresponding connection to the tap position of the power supply tap voltage. If it is variable flux regulation, because each tap position when the no-load loss is not the same, must be based on the technical conditions, select the correct tap position, apply the specified rated voltage, because in the variable flux regulation, the primary side is always added to a voltage in the various tap position.
It is generally required that the waveform of the applied voltage must be an approximate sinusoidal waveform. Therefore, one is a harmonic analyser to measure the harmonic component contained in the voltage waveform, the second is a simple method, with an average voltmeter, but the scale for the rms voltmeter to measure the voltage, and the rms voltmeter readings compared to the difference between the two is greater than 3%, indicating that the voltage waveform is not sinusoidal, measured no-load losses, according to the requirements of the new standard should be invalidated.
For the measurement system, it is necessary to select the appropriate test line, select the appropriate test equipment and instrumentation. Because of the development of permeability materials, the wattage per kilogram loss in a substantial decline in manufacturing plants are selected high-quality high permeability grain-oriented silicon steel sheet or even select amorphous alloys as permeability materials, structure and the development of such as stepped seams and the full slope of the non-porous, the process of using non-stacking on the iron yoke process, manufacturers are in the development of low-loss transformers, especially the no-load loss has been a substantial decline. Therefore, the measurement system puts forward new requirements. Capacity remains unchanged, no-load loss decline means that no-load transformer power factor decline, power factor is small requires manufacturers to change and transform the measurement system. It is appropriate to use three wattmeter method, choose 0.05-0.1 level transformer, choose nooks and low power factor wattmeter, only in this way, to ensure the accuracy of the measurement. In the power factor of 0.01, the phase difference of the transformer is 1 minute will cause power error of 2.9%. Therefore, in the actual measurement, but also the correct choice of current transformer and voltage transformer current ratio and voltage ratio. The actual current is much smaller than the current transformer connected to the current, the current transformer phase difference and current error is greater, which will lead to a larger error in the actual measurement results, so the current drawn by the transformer should be close to the rated current of the current transformer.
In addition, in the design according to the specified procedures, with reference to the selected silicon steel sheet unit loss and process coefficients calculated by the no-load loss, generally called the calculated value. This value should be compared with the standard value specified in the standard or with the standard value specified in the contract or the guaranteed value. Calculated value must be less than the standard value or guaranteed value, can not eat in the calculation of the margin, especially the batch of transformers. In addition, the calculated value is only valid for the designer or within the design section, there is no legal effect, you can not use the calculated value to judge the loss level of the product. The standard values specified in the standard or the guaranteed values specified in the contract have a legal effect. Products exceeding the standard value plus the permissible deviation, or called the guaranteed value (guaranteed value equal to the standard value plus the permissible deviation) are unqualified products. If there is a loss evaluation system, generally in the contract will be pointed out, especially export products, more than the specified loss value to be fined, no-load loss of the highest fines, the loss of European countries can be seen in the loss of evaluation value of “Transformer” magazine, Issue 11, 1994. Each kilowatt to be fined several thousand dollars. This is the legal effect, and directly linked to economic efficiency.
The concept of measured value should also be correctly understood, not the readings of the hut meter (or called power converter readings) is the measured value to be converted to rated conditions, and to have sufficient accuracy. Measured value of no-load losses, mainly the power supply voltage waveform to sinusoidal, average voltmeter readings and rms voltage readings of less than 3%.
Five
No-load loss, load loss, impedance voltage calculation
No-load loss: when the transformer secondary winding open circuit, the primary winding applied to the rated frequency sinusoidal waveform of the rated voltage, the active power consumed is called no-load loss.
The algorithm is as follows:
No-load loss = no-load loss process coefficient × unit loss × core
Load loss: when the transformer secondary winding short circuit (steady state), the primary winding circulating rated current consumed active power is called load loss.
Algorithm is as follows:
Load loss = the largest pair of winding resistance loss + additional loss
Additional loss = winding eddy current loss + parallel winding wire circulation loss + stray loss + lead loss
Impedance voltage: when the transformer secondary winding short circuit (steady state), the primary winding circulating rated current and the applied voltage is called impedance voltage Uz. usually Uz to the rated voltage expressed as a percentage, i.e., uz = (Uz/U1n) * 100%
Turns potential: u = 4.44 * f * B * At, V
Where: B – magnetic density in the core, TAt – core effective cross-sectional area, square metres
Can be transformed into a transformer design calculations commonly used formulas:
When f=50Hz: u=B*At/450*10^5,V
When f=60Hz: u=B*At/375*10^5,V
If the phase voltage and the number of turns are known, the turn potential is equal to the phase voltage divided by the number of turns Transformer no-load loss calculation – transformer no-load loss composition.
No-load losses include hysteresis and eddy current losses in the iron core and no-load current losses in the primary coil resistance, the former is called iron loss latter is called copper loss. As the no-load current is very small, the latter can be ignored, therefore, no-load loss is basically iron loss.
Influence transformer no-load loss iron loss of many factors, expressed in mathematical form, then the type of
Pn, Pw – said hysteresis losses and eddy current losses kn, kw – constant
f – the frequency of the transformer external voltage H
Bm – maximum magnetic flux density in the core We/m2
n – Shjeinmetz constant, for commonly used silicon steel sheet, when Bm = (1.0 ~ 1.6) We / m 2, n ≈ 2, for the current use of directional silicon steel sheet, take 2.5 ~ 3.5.
According to the theoretical analysis of the transformer, assuming that the primary induced potential is E1 (volts), then: E1 = KfBm
K is a constant of proportionality, by the number of primary turns and core cross-sectional area.
As the primary leakage impedance voltage drop is very small, if ignored, then E1 = U1
Visible, transformer no-load loss iron loss and external voltage has a great relationship if the voltage V for a certain value, the transformer no-load loss iron loss is unchanged, (because f unchanged), but also because of the normal operation of U1 = U1N, so the no-load loss is also known as unchanged loss. If the voltage fluctuation, the no-load loss that change. Transformer iron loss and iron core material and manufacturing process, and load size has nothing to do.