Apparatus for energizing a protective device, and associated method

An improved overload relay includes a number of current transformers that draw power from a circuit it protects to power itself. The current transformers charge a capacitor which powers a processor and which can energize a solenoid to initiate the interruption of the circuit. The overload relay further includes a capacitor analysis circuit which detects an operational parameter of the capacitor and enables a processor to determine when the energy storage capability of the capacitor has dropped to a predetermined threshold. In the event of such a determination, the overload relay can perform any of a number of actions.

BACKGROUND

The disclosed and claimed concept relates generally to an apparatus that is configured to energize a protective device to open at least a portion of a circuit and, more particularly, to an apparatus that performs a predetermined action when its ability to initiate the opening of the circuit has dropped to a predetermined threshold.

2. Description of the Related Art

Numerous types of circuit interrupters are known. One type of circuit interrupter is in the form of a relay that includes an current measurement circuit that employs various algorithms to determine when to disconnect the power to a large load, such as a motor, in certain predefined overload scenarios. Such circuit interrupters may include an energy storage device such as an electrolytic capacitor to energize a solenoid of a relay which causes another solenoid to change state to cause a contactor to interrupt the circuit. While such circuit interrupters have generally been effective for their intended purposes, such circuit interrupters have not been without limitation.

As is generally understood, the energy storage capability of an electrolytic capacitor can degrade over time, and elevated temperatures can accelerate such degradation. Depending upon the degree of degradation, such a capacitor may store an insufficient amount of energy to energize the solenoid that initiates the opening of the circuit. Moreover, while certain overload conditions can occur in an extremely short period of time, other overload conditions develop over several minutes or even hours, and it is generally undesirable for equipment to suddenly stop operating, whether because the power supply to the equipment has been interrupted or because the equipment has overheated or otherwise failed. It thus would be desirable to address these and other shortcomings known in the relevant art.

SUMMARY

Accordingly, an improved apparatus in the form of an overload relay includes a number of current transformers that draw power from a circuit it protects in order to evaluate the circuit and also to power itself. The current transformers charge a capacitor which powers a processor and which can energize a solenoid to toggle a normally CLOSED set of contacts to an OPEN condition to cause another solenoid to open a contactor to interrupt the circuit to a load. Advantageously, the overload relay further includes a capacitor analysis circuit which detects one or more operational parameters of the capacitor and enables a processor of the overload relay to determine when the energy storage capability of the capacitor has dropped to a predetermined threshold. In the event of such a determination, the overload relay can perform any of a number of predetermined actions, such as sending an indication that the overload relay or the capacitor itself should be replaced in a given period of time or by causing the capacitor to energize the solenoid to interrupt the circuit. The overload relay further advantageously includes a visual indicator that includes an LED that is able to provide a visual indication of a status of the overload relay.

Accordingly, an aspect of the disclosed and claimed concept is to provide an improved overload relay that is self-powered and that includes a visual indicator that provides an indication of a status of the overload relay.

Another aspect of the disclosed and claimed concept is to provide an improved overload relay that is configured to protect a circuit and that provides an indication of its potential inability to protect the circuit.

These and other aspects of the disclosed and claimed concept are provided by an improved apparatus that is structured to energize a protective device to at least initiate an opening of at least a portion of a circuit. The general nature of the apparatus can be stated as including a storage device structured to store energy and to release at least a portion of the energy to energize the protective device, a detection system connected with the storage device and structured to detect at least a first operational parameter of the storage device that is usable in determining an energy storage capability of the storage device and, responsive to a determination by the apparatus that the energy storage capability of the storage device has dropped to a predetermined threshold, the apparatus being structured to perform a predetermined action.

Still other aspects of the disclosed and claimed concept are provided by an improved method of indicating a need to replace an apparatus that is structured to energize a protective device to at least initiate an opening of at least a portion of a circuit. The general nature of the method can be stated as including storing energy in a storage device to enable a release of at least a portion of the energy to energize the protective device, detecting at least a first operational parameter of the storage device that is usable in determining an energy storage capability of the storage device and, responsive to a determination by the apparatus that the energy storage capability of the storage device has dropped to a predetermined threshold, performing a predetermined action.

DESCRIPTION

An improved overload relay4in accordance with the disclosed and claimed concept is depicted schematically inFIG. 1. The overload relay4monitors and controls a circuit that comprises three phases8A,8B, and8C, collectively referred to hereinafter with the numeral8, that extend between a power source12and a load16which, in the depicted exemplary embodiment, is an electric motor. The circuit also includes a main disconnect20that can be manually operated as well as a contactor apparatus24that is operated by the overload relay4to interrupt the circuit.

The overload relay4comprises a housing26upon which are disposed three current transformers28A,28B, and28C, collectively referred to hereinafter with the numeral28, which are used to monitor the current through the phases8and to power at least a portion of the overload relay4. In powering the overload relay, the current that is drawn from the phases8by the current transformers28is delivered to a boost regulator32and then to a storage device which, in the exemplary embodiment herein, is in the form of an electrolytic capacitor36. Current drawn from the phases8by the current transformers28is stored in the capacitor36which, in turn, powers various functions of the overload relay4.

The current transformers28are additionally connected with a current measurement circuit40that is connected with a processor44. The current measurement circuit40enables the processor44to monitor the current in the phases8and to take action in certain predetermined circumstances. The processor44has numerous algorithms incorporated thereon to evaluate the amount of current flowing through the phases8as a function of time and it is configured to interrupt the circuit when needed. For instance, the processor44might employ an algorithm whereby current is monitored over time as an indication of the temperature of the motor. If the current flowing through the circuit is at a sufficient level for a sufficient period of time, the processor44might determine that the load16is in danger of overheating and will determine that the circuit should be interrupted, by way of example.

Advantageously, the overload relay4further comprises a capacitor analysis circuit48which serves as a detection system to detect certain operational parameters of the capacitor36, such as its voltage. WhileFIG. 1schematically depicts the capacitor analysis circuit48as being interposed electrically between the capacitor36and the processor44, it is understood that other connection arrangements can be employed without departing from the present concept. The operation of the capacitor analysis circuit48will be discussed in greater detail elsewhere herein.

The overload relay4further comprises a protective device in the form of a solenoid52which is of a latching type. In certain predefined circumstances, the processor44can cause the solenoid52to be energized by the capacitor36to toggle a set of normally CLOSED contacts56to an OPEN condition and to toggle a set of normally OPEN contacts60to a CLOSED condition. Since the solenoid52is of a latching type, a pulse of energy from the capacitor36causes the solenoid52to change states and thus to toggle the normally CLOSED contacts56and the normally OPEN contacts60to their OPEN and CLOSED alternate conditions, respectively, regardless of whether the energy from the capacitor36ceases. That is, another pulse of energy or a mechanical reset is required to cause the solenoid52to return to its original, i.e., normal condition and to toggle the normally CLOSED contacts56and the normally OPEN contacts60to their CLOSED and OPEN normal conditions, respectively.

When the solenoid52is energized and toggles the normally OPEN contacts60to their CLOSED condition, an indicator64is energized, and the indicator64can be in the form of a light, an alarm, etc. When the normally CLOSED contacts56are toggled by the solenoid52to their OPEN condition, it interrupts an operating current that had been flowing through the normally CLOSED contacts56to a solenoid68of the contactor apparatus24, and such interruption of the operating current causes the solenoid68to change state and to operate the contactor, which interrupts the circuit to the load16. The solenoid68is of a non-latching type, such that the interruption of operating current to the solenoid68due to the normally CLOSED contacts56being toggled to their OPEN condition causes the solenoid68to change states and interrupt the circuit.

The overload relay4further advantageously comprises an indictor which, in the exemplary embodiment depicted herein, is a visual indicator72that comprises an illumination source and a secondary, mechanical indicator. It is understood, however, that the visual indicator72could alternately or additionally include an audible indicator component without departing from the present concept. The illumination source is the exemplary embodiment depicted herein is an LED76that is powered by the capacitor36from current drawn from the circuit by the current transformers28. The secondary indicator is in the form of an exemplary mechanical reset80which physically moves when the solenoid52changes state. That is, when the solenoid52is in a first state, the mechanical reset80is in a first physical position, as is depicted schematically in solid lines inFIG. 1. However, if the solenoid52is energized by the capacitor36and is caused to change state to a second state, the mechanical reset80physically moves to another position, as is indicated in dashed lines at the numeral82, which can be visually ascertained by a technician.

The overload relay4further comprises a communications interface84and a user interface88connected with the processor44that enable interaction with the overload relay4. For instance, the communications interface84can be used to communicate signals to a remote device such as a sensor or a computer device, by way of example. The user interface88can be used to connect with a remote computer device or other apparatus to enable a technician to interact with the overload relay4to operate the overload relay4or to receive data from the overload relay4, or both, by way of example.

Advantageously, the LED76can provide visual indications of any of a plurality of statuses of the overload relay4. For instance, since the LED76is self-powered, i.e., is powered by current drawn by the current transformers28from the phases8of the circuit, the LED76will be in an unilluminated condition, i.e., will be dark, during the initial charging of the capacitor36. That is, the LED76will be unilluminated when the capacitor36has stored therein insufficient energy to energize the solenoid52, which is one status of the overload relay4.

Once the capacitor36has reached a desirable level of charge and has stored therein enough energy to reliably energize the solenoid52, the LED76is caused to blink in a first predetermined fashion. For instance, the LED76can be caused to blink one time per second, by way of example, to indicate that the capacitor36is charged and that the overload relay4is functioning properly. This is another status of the overload relay4.

Depending upon the output from the current measurement circuit40, the processor44may cause the LED to blink in a second, predetermined fashion if a trip condition is imminent but has not yet occurred. By way of example, the LED76can be caused to blink twice per second, which would indicate still another status of the overload relay4.

In the event that the capacitor36is caused by the processor44to energize the solenoid52and interrupt the circuit, the LED76likely will again be unilluminated since current is not flowing through the phases8and the capacitor36will have been substantially discharged from its energizing of the solenoid52. However, since the mechanical reset80will move to its second position, as is indicated at the numeral82, the second position of the mechanical reset80in combination with the LED76being in an unilluminated condition will indicate yet another status of the overload relay. In this regard, it is understood that an unilluminated condition of the LED76in combination with the mechanical reset80being in its first position (as is indicated at the numeral80inFIG. 1) is what typically will serve as the indication that the status of the overload relay4is that of being in an initial charging condition with the capacitor36being less than fully charged. It is also understood that the various statuses of the overload relay4can be communicated to another device via the communications interface84.

Further advantageously, the capacitor analysis circuit48is operable to determine the energy storage capability of the capacitor36in order to generate an alarm or perform some type of predetermined action when the energy storage capability has dropped to a predetermined threshold. The predetermined threshold typically will be just above the amount of energy required to energize the solenoid52. That is, the predetermined action is performed if the capacitor36reaches a condition where its ability to energize the solenoid52is potentially questionable.

The capacitor analysis circuit48can evaluate the energy storage capability of the capacitor36in any of a variety of fashions. For instance, the capacitor analysis circuit48may partially discharge the capacitor36and detect the voltage at one or more times during the at least partial discharging process. By way of further example, the capacitor analysis circuit48may cause the capacitor36to be charged at an energy storage level greater than that to which it is typically charged and may evaluate the degree to which the capacitor36maintains the extra charge by evaluating the voltage of the capacitor36as a function of time. Numerous other methodologies can be envisioned, such as those wherein evaluation of the capacitor36occurs without directly monitoring any of the characteristics of the capacitor36. Rather, such an evaluation of the capacitor36could involve the evaluation of other factors such as the duration of time during which the capacitor36has been in service, the ambient temperature over time, the number of charge/discharge cycles of the capacitor36, etc., by way of example.

Advantageously, if the capacitor36is determined to have an energy storage capability that has dropped to a predetermined threshold, the processor44can trigger a visual alarm, an audible alarm, or both, and/or can communicate a signal over the communications interface84to another device. Additionally or alternatively, the processor44can trigger the capacitor36to energize the solenoid52and interrupt the circuit. Furthermore, the LED76can be triggered to blink or be otherwise illuminated in still another fashion, such as to blink three times per second, by way of example. Other predetermined actions can be envisioned.

It is understood that the processor44or the capacitor analysis circuit48or both can be involved in the determination that the energy storage capability of the capacitor36has dropped to the predetermined threshold. It is also understood that other criteria can be employed in determining whether the capacitor36or the overload relay4itself should be replaced.

The predetermined action that is taken by the overload relay4in response to a determination that the energy storage capability of the capacitor36has dropped to a predetermined threshold can be interpreted in any of a variety of fashions. By way of example, the visual or audible alarm may indicate the need to replace the capacitor36or the overload relay4within ninety days or at the next scheduled maintenance cycle. Alternatively, the communications interface84may be employed to communicate to another device a message representative of a warning that the capacitor36or the overload relay4itself should be replaced within ninety days. Further advantageously, the processor44can receive input from the current measurement circuit40to provide a further indication that the capacitor36or the overload relay4itself should be replaced immediately. In such a scenario, the initial warning of replacement in ninety days may have been initially provided, but the temperature conditions of the load16, and thus potentially the ambient conditions, may have been determined by the current measurement circuit40to be such that a more immediate replacement of the capacitor36or the overload relay4itself may be required.

The LED76is disposed on the housing26but can alternatively be disposed elsewhere or can be in the form of a plurality of LEDs disposed in various locations on and remote from the housing26. Thus, a technician looking at the overload relay4, and thus the housing26, can advantageously ascertain a status of the overload relay4.

An improved method of operating the overload relay4is depicted generally inFIG. 2. Energy is stored, as at104, in a storage device such as the capacitor36. An analysis operation is performed, as at108, on the capacitor36, with one or more operational parameters of the capacitor36being detected, as at112. If, as at116, it is determined that the energy storage capability of the capacitor36has dropped to a predetermined threshold, a predetermined action is performed, as at120. As mentioned elsewhere herein, examples of such a predetermined action would include any one or more of the triggering of a visual alarm, the triggering of an audible alarm, the communicating of a signal over a communications interface to another device, and the energizing of a protective device such as the solenoid52. Other predetermined actions will be apparent.

Another flowchart depicting other advantageous features of the overload relay4is depicted generally inFIG. 3. A visual indicator such as would include the LED76is self-powered, as at204, such as by employing the current transformers28to draw current from the circuit that is being protected by the overload relay4. At least a first visual indication is provided, as at208, that is representative of a status of the overload relay4. As mentioned elsewhere herein, the LED76can blink in any of a variety of fashions or can be unilluminated. When the LED76is unilluminated, the condition of the mechanical reset80can be used to determine whether the overload relay4is in an initial charging condition or whether it has already tripped. It is understood that the visual indications can be supplemented by further communications provided to an external device via the communications interface84.