GB2139388A - Method and apparatus for protecting a hydraulic machine - Google Patents

Abstract

The difference in temperature across the fluid inlet and the fluid outlet of the machine is taken and used to actuate means to signify when the machine is operating outside of its required performance. In a preferred embodiment the temperature difference DELTA T is evaluated from the equation <IMAGE> where the efficiency @ /p, the head H in metres and the temperature t2 of the fluid are all known.

Description

SPECIFICATION Protection for hydraulic machines This invention relates to protection for hydraulic machines, that is to say protection for pumps, motors, turbines and the like.

Protection is to be understood to mean a safeguard for the hydraulic machine so that it may function according to its design performance limits and not move outside of said limits into malfunction without giving a warning to an engineer in charge of its operation.

It has been known since c. 1 914 that the efficiency of a hydraulic machine may be estimated by a determination of the small differences in the fluid temperature between the inlet and the outlet of the machine in relation to the fluid head between said inlet and said outlet.

This is generally expressed mathematically in the convenient form enunciated: WILLM. G. and CAMPMAS.P. in an article entitled Efficiency measurements for hydraulic turbines by the Poirson Thermometric method translated into English in Supplement No.6/1956 from La Houille Blanche 9(1954) p449/550, and from BARBILLION.L. Méthode thermometrique de mesure du rendement des turbines hydrauliques Revue Generale del'6lectri- cité 26(1929) p487-497.

The theory of the thermometric or thermodynamic method is as follows: Efficiency in a hydraulic pump for example may be expressed as Work Done or Wo Effort W1 but W1 = W0 + Losses.

1 #p = 1 + Losses WO thus providing one can determine the term Losses.

WO 71p may be calculated.

Some of the energy that is lost in pumping may go to drain through gland water or bearing cooling water but the majority of it is dissipated as heat in the pumped fluid.

The energy dissipated as heat is defined as Cp OAT where Cp is the Specific heat of the Fluid Q is the Flow AT is the Temperature rise across the pump Hence Losses = Cp OAT WO gQH and therefore 1 #p = 1 + Cp#T gH an expression that is totally independent of flow, taking Cp as 4186 and g as 9.81 we have #p = 1 1 + 426.7#T H The above equation is simplified as it assumes constant thermodynamic properties for the pumped fluid. The full equation is given by Foord.T.R. et al. Thermometric Method of Measuring Hydraulic Efficiency. Water Power. Oct (1964) p432-434.

Vo(P - P)(1 - ss) + g(V2 - V1) + (Z2 - Z1) = t Vo(P2 - P1)(1 - a) + jCp2(t2 - t1) + g(V22 - V12) + (Z2 - Z1) Where P is pressure; t temperature; V velocity; Z pressure-gauge height; C specific heat of water at constant pressure; V the specific volume of water at 4 C, 760mm Hg; J the mechanical equivalent of heat. The suffixes 1 and 2 refer to the inlet and outlet respectively. a and ss are thermodynamic factors based on the chosen value for V0 and are obtained from published charts. The value of a for water is zero at 4 C rising to about 0.044 at 15 C. In practice, P is usually small and can be neglected.

Under the following conditions the above equation # may be simplified whilst still retaining a high degree of accuracy.

Conditions P2 - p1 +g(V2 - V1) + (Z2 - Z1) 1 0'C < t2 < 50 C Formula (1) becomes 1 #p = --------------------- 1.0189-0.0041t2+426.7#T (2) H H If we consider a pump in which: Q the flow is 400m3/hr Head is 100m Efficiency 7p is 80% Temperature of fluid is 11 C Then from equation (2) above the temperature rise across the pump, AT is 0.065 C that is 65 millidegrees Celsius.

It is unnecessary with this estimation of efficiency to know the flow characteristics of the machine.

I have surprisingly found according to the present invention that for the protection per se of hydraulic machines it is sufficient to take the difference in temperature across the fluid inlet and fluid outlet of the hydraulic machines to obtain a small temperature difference that can effectively actuate means effectively to protect said hydraulic machine. In one embodiment means are provided that are electrically actuated by a temperature difference AT evaluated by the formula 1 #p = --------------------- 1.0189-0.0041t2+426.7#T H H where the efficiency 71p, the head H in metres and the temperature of the fluid t2 are known.

In yet a further embodiment the value of the difference in temperature is divided electrically by the value of the differential pressure of the hydraulic machine to give a non-dimensional term that can give a signal that can be used to protect said machine.

Ideally electrical signals from two probes are electrically substracted and the resultant signal fed into a micro-processor to evaluate the signal and relate it with the desired signal. The signal so produced is then deployed as a protection signal which, depending upon its value, will show when the hydraulic machine is working within the correct limits of its design. The protection signal may sound an alarm or switch off the hydraulic machine once that signal is above or below safe and correct working conditions for the machine.

The invention will be more fully understood from the following description given by way of example only with reference to the figures of the accompanying drawings in which: Figure 1 is a circuit diagram of a differential temperature measurement means for a protection device using two terminal integrated circuit temperature transducer; and Figure 2 is a block diagram of a hydraulic machine protection device.

Referring now to Fig. 1 there is shown: The two AD590 devices shown are two terminal integrated circuit temperature transducers made by analog devices P.O. Box 280 Norwood Massachusetts 02062 United States of America.

These transducers produce an output current proportional to absolute temperature.

For supply voltages between + 4V and + 30V these devices act as a high impedance, constant current regulator passing 1 microamp/degree celsius.

The circuit of Fig. 1 demonstrates one method by which differential temperature measurements can be made.

R1 and R2 are used to trim the operational amplifier to take into account any manufacturing tolerance in the AD590 themselves.

The modus operandi of the circuit is as follows.

T1 responds to the fluid outlet temperature and T2 responds to the fluid inlet temperature of the machine.

The configuration of T1 and T2 shown produces a small current which is a combination of the absolute temperature difference between T1 and T2 and the unavoidable manufacturing tolerances between AD590 (T1) and AD590 (T2).

The manufacturing tolerance is corrected by means of R1 and R2.

The resulting current signal is then converted into a voltage signal by way of the operational amplifier AD741.

The device of Fig. 2 may be employed in the measurement of relative performance of hydraulic machines and related to their overall protection.

Consider the example of a pump as referred to above which is pumping water nbt at 11 C but at 4 C then it generates at a hydraulic head of 100 metres and an efficiency of 80% a temperature rise of 0.058 C.

If a malfunction of this pump is such that the pump now generates a hydraulic head of 200 metres at an efficiency of 40% then the temperature rise will be 0.0703 C.

Thus whilst the head has increased by a factor of two and the efficiency has halved the differential temperature has increased by a factor of 1 2.5.

This amplification effect of the change in running conditions is the basic principle of my pump protection unit.

Such a system may contain a cost penalty feature by the inclusion of pressure signals into the temperature differential and specific heat equation.

The accuracy of the protection device may be improved by incorporating a pressure signal into the device.

For example again using the previous formulae with the following pumping conditions.

Generated head 1 00M efficiency 80% water temperature 4 degrees differential temperature 0.058 C.

If the conditions now change such that the head generated is only 80 metres but the differential temperature is unchanged then the efficiency of the pump is 67%.

In this instance a change in pumping conditions has not produced a change in differential temperature measurement.

If, however, we now incorporate the differential pressure signal into the equation such that the differential temperature signal is divided by the differential pressure signal then the following result is achieved.

Case 1 Differential Temperature 58 = 100=0.58 Differential Pressure Case 2 Differential Temperature 58 = 100=1.16 Differential Pressure This change in signal is sufficient to operate the control systems.

Claims (6)

1. A method for the protection of a hydraulic machine wherein the difference in temperature across the fluid inlet and the fluid outlet of the hydraulic machine is taken and used to actuate means effectively to signify when the hydraulic machine is operating outside of its required performance.

2. The method as claimed in Claim 1 wherein said means is actuated by a temperature difference AT evaluated by the formula XP = 1.0189 - 0.0041t2 + 426.7AT H where the efficiency lIp the head H in metres and the temperature t2 of the fluid are all known.

3. The method as claimed in Claim 1 or Claim 2 wherein the temperature difference by the value of the differential pressure of the hydraulic machine to provide a signal to actuate the said means.

4. The method as claimed in Claim 3 wherein the division is performed electrically.

5. A method as hereinbefore described.

6. Apparatus for carrying out the method of Claim 5, said apparatus being constructed and arranged substantially as hereinbefore described and as shown in the figures of the accompanying drawings.