rel="canonical" href="https://www.selfstudyworld.com/" /> Hopkinson Test Skip to main content

Hopkinson Test

Hopkinson Test

Hopkinson Test requires two identical shunt machines which are coupled mechanically and also connected electrically in parallel. One of them acts as a motor and the other as a generator.

  • The motor takes its input from the supply.
  • The mechanical output of the motor drives the generator and the electrical output of the generator is used in supplying the input to the motor.
  • Thus, the output of each machine is fed as input to the other.
  • When both machines are run on full load, the input from the supply will be equal to the total losses of both machines.
  • Hence the power input from the supply is very small.


This test is also called
(a) regenerative test
(b) back-to-back test
(c) heat-run test

Hopkinson Test Circuit Diagram

Hopkinson Test 

  • The circuit diagram for the Hopkinson test is shown in Fig. 7.29 machine M is started from the supply as a motor with the help of a starter (not shown).
  • The switch S is kept open.
  • The field current of M is adjusted with the help of field rheostat RM to enable the motor to run at the rated speed.
  • Machine G acts as a generator. Since G is mechanically coupled to M, it runs at the rated speed of M. 
  • The excitation of the generator G is so adjusted with the help of its field rheostat RG that the voltage across the armature of G is slightly higher than the supply voltage.
  • In actual practice, the terminal voltage of the generator is kept 1 or 2V higher than the supply busbar voltage.
  • When this is achieved, that is, the voltage of the generator is equal and of the same polarity as the busbar voltage, the main switch S is closed and the generator is connected to the busbars.
  • Thus, both machines are now parallel across the supply. Under this condition, the generator is said to float. That is, it is neither taking any current from nor giving any current to the supply.
  • Any required load can now be thrown on the machines by adjusting the excitation of the machines with the help of field rheostats

The efficiency of the Machine by Hopkinson Test

Efficiency of the Machine by Hopkinson’s Test 

 

efficiency of the Generator And Motor 

The efficiency of the Generator And Motor 


Advantages of Hopkinson Test

  1. The main advantages of using the Hopkinson test for the determination of efficiency.
  2. The total power taken from the supply is meager. Therefore this method is very economical.
  3. The temperature rise and the commutation conditions can be checked under rated load conditions.
  4. stray losses are considered, as both the machines are operated under rated load conditions.
  5. Large machines can be tested at rated loads without consuming much power from the supply.
  6. Efficiency at different loads can be determined.

Disadvantages of Hopkinson Test

The main disadvantage of this method is the necessity of two practically identical machines to be available. Consequently, this test is suitable for manufacturers of large de machines.

Popular posts from this blog

Limitations of Terzaghi Theory

Limitations of Terzaghi Theory The value of the coefficient of consolidation has been assumed to be constant.  The distance d of the drainage path cannot be measured accurately in the field. The thickness of the deposit is generally variable, and an average value has to be estimated.  There is sometimes difficulty 1n locating the drainage face, sometimes thin previous seams that can act as good drainage face are missed in the boring operations. The equation is based on the assumption that the consolidation is one-dimensional. In the field, the consolidation is generally 3-dimensional. The lateral drainage may have a significant effect on the time rate of consolidation. The initial consolidation and secondary consolidation have been neglected. Sometimes these form an important part of the total consolidation. In actual practice, the pressure distribution may be far from linear or uniform. Read More Muller-Breslau principle

Price Guard Wire Method

Price Guard Wire Method Some form of  Price Guard Wire Method  is generally used to eliminate the errors caused by leakage currents over insulation. Fig. 3.14 illustrates the operation of This Method. In fig 3.14(a), a high resistance mounted on a piece of insulating material is measured by the ammeter voltmeter method. The micro-ammeter measures the sum of the current through the resistor (IR) and the current through the leakage path around the resistor. The measured value of resistance computed from the readings indicated on the voltmeter and the microammeter, will not be a true value but will be in error.   Figure 3.14 Application of  guard  circuit for measurement of high resistance In fig, 3.14 (b), the  guard  terminal has been added to the resistance terminal block. The  guard  terminal surrounds the resistance terminal entirely and is connected to the battery side of the micro-ammeter. The leakage current IL now

Streamer Theory of Breakdown in Gases

Streamer Theory of Breakdown in Gases According to the Townsend theory firstly, current growth occurs as a result of the ionization process only. But in practice, breakdown voltages were found to depend on the gas pressure and the geometry of the gap. Second chances time lags of the order of 10-5 s, but practically it was observed to occur at a very short time of 10-8 s. Also, the Townsend mechanism predicts a very diffused form of discharge, that actually discharges were found to be filamentary and irregular. Townsend's mechanism failed to explain all these observed phenomena and as a result, The Streamer theory was proposed. The theory predicts the development of a spark discharge directly from a single avalanche in which the space charge developed by the avalanche itself is said to transform the avalanche into a plasma steamer. In Fig 1.7, a single electron starting at the cathode by ionization builds up an avalanche that crosses the gap. The electrons in the a