SYSTEM INCLUDING THE SAME CROSS REFERENCE TO RELATED APPLICATION

This application claims the enefit of US. Patent Application Serial No. 13/419,776, filed March 14, 2012, which is incorporated by reference herein.

BACKGROUND

Field

The disclosed concept pertains generally to electrical switching apparatus and, more particularly, to trip units providing zone interlocking for such apparatus. The disclosed concept further pertains to electrical switching apparatus providing zone interlocking. The disclosed concept also pertains to systems providing z ne interlocking.

Background Information

Circuit interrupters, such as for example and without limitation, circuit breakers, are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition, a short circuit, or another fault condition, such, as an arc fault or a ground fault. Molded case circuit breakers typically include a pair of separable contacts per phase. The separable contacts may be operated either manually by way of a handle disposed on the outside of the case or automatically in response to a detected fault condition. Typically, such circuit breakers include an operating mechanism, which is designed to rapidly open and close the separable contacts, and a trip mechanism, such as a trip unit, which senses a number of fault conditions to trip the breaker automatically. Upon sensing a fault condition, the trip unit trips th operating mechanism to a tri state, which moves the separable contacts to their open position.

Typically, two or more circuit interrupters are placed between a fault and ihe so urce of the fault current. In order to minimize electrical service interruption, the circuit interrupters are selective in response such that the one nearest the fault will first attempt to interrupt the fault current. If this circuit interrupter does not timely clear the fault, then the next upstream circuit interrupter will attempt io do so, and so on. This response selectivity is sometimes termed system selective coordination.

Zone selective interlocking (ZSI) (e.g., also known as "zone interlocking" ^' ) is a method of controlling circuit interrupters in order to provide selectivity with relatively very short delay times, irrespective of the number of zones (e.g., without limitation, a Hue side zone; a load side zone; a number of upstream

/ones; a number of do wns tream zones; a number of grading levels) and the location of a fault in a power distribution system. A ZSI input (ZSI IN) and a ZSI output (ZSi_OUT) are provided at each circuit interrupter. Interlocking may be applied to faults between phases or earth-faults or both.

As one example, zone interlocking uses a ZSl_OUT / ZSIJflN

communication scheme to connect line and toad circuit interrupter trip units together. When a fault occurs, the trip units communicate using a ZSI OUT ZSi J

hardwired connection to determine which load side circuit interrupter is ciosest to the fault. The trip unit in the circuit interrupter closest to the fault overrides any

customer-defined delay and opens instantaneously, thereby clearing the fault and allowing the line side circuit interrupters to remain closed.

if ZSI is used in several zones, then each circuit interrupter affected by, for example, a short circuit current (i.e., upstream of the fault) interrogates the circuit interrupters) directl downstream of that affected circuit interrupter to determine whether the short circuit current is present in or is aff ecting the adjacent downstream one, A delay setting t¾¾ is adjusted at each circuit interrupter to ensure that the downstream circuit interrupter, directly upstream of the fault, has time to interrupt, the fault current. The advantages of ZSI increase with additional zones, since time-based selectivity can result in unacceptably long delays at the upstream power source end of the system.

Each of the circuit interrupters in a distribution system is typically sized in order that they can achieve selective coordination. More often than not, upstream circuit interrupters have to be oversized.

Although the use of ZSIJN and ZSi _m OUT signals help to accomplish, certain aspects of coordination, they require hardwiring between downstream and upstream circuit interrupters. There is a need for short circuit zone location detection thai allows circuit interrupters to act autonomously.

There is room for improvement in trip units for electrical switching apparatus.

There is also room for improvement in electrical switching apparatus.

There is further room for improvement in systems including electrical switching apparatus.

SUMMARY

These needs and others are met by embodiments of the disclosed concept, for which a routine of a trip unit processor is structured to input a sensed value of current from a current: sensor, determine if the sensed value of current exceeds a predetermined value and respomively cause a transmitter to transmit second frequency pulses having a second frequency to a conductor, monitor within a predetermined time after determining that die sensed value of current exceeds the predetermined value if a number of first frequency pulses having a number of first frequencies is received by a circuit from the conductor, and responsively delay outputting a trip signal, and, otherwise, immediately output the trip signal

in accordance with one aspect of the disclosed concept, a trip unit comprises: a current sensor structured to sense a value of current flowing through a conductor; a circuit structured to receive first frequency pulses having a number of first frequencies from the conductor: a transmitter structured to transmit second frequency pulses having a second frequency to the conductor, the second frequency being different than, the number of first frequencies; and a processor comprising a routine structured to input the sensed value of current from the current sensor, determine if the sensed value of current exceeds a predetermined value and

responsive] y cause the transmitter to transmit the second frequency pulses having the second frequency to the conductor, monitor within a predetermined time after determining thai the sensed value of current exceeds the predetermined value if a n umber of the first frequency pulses having the number of first frequencies is received by the circuit from the conductor, and responsively delay outputting a trip signal, and, otherwise, immediately output the trip signal. As another aspect of the disclosed concept, an electrical switching apparatus comprises: separable contacts; an operating mechanism, structured to open and close the separable contacts; a trip mechanism cooperating with the operating mechanism to trip open the separable contacts, the trip mechanism comprising; a current sensor structured to sense a value of current flowing through the separable con tacts, a. circuit structured to receive first frequency pulses having a number of .first frequencies from, a conductor in series with the separable contacts, a transmitter structured to transmit second frequency pulses having a second frequency to the conductor, the second frequency being different than the number of first frequencies, and a processor comprising a routine structured to input, the sensed value of current from the current sensor, determine if the sensed value of current exceeds a predetermined value and responsiveiy cause the transmitter to transmit the second frequency pulses having the second frequency to the conductor, monitor within a predetermined time after determining that the sensed value of current exceeds the predetermined value if a number of the first frequency poises having the number of first frequencies is received by the circuit from the conductor, and. responsiveiy delay outputting a trip signal, and, otherwise, immediately output the trip signal

As another aspect of the disclosed concept, a system comprises: a first branch level comprising a number of first electrical switching apparatus; and a second branch, level downstream of the first branch level and comprising a number of second electrical s witchin apparatus, wherein each of the number of first elec trical sw itching apparatus and the number of second electrical switching apparatus comprises:

separable contacts, an. operating mechanism, structured t open, and close the separable contacts, and a trip mechanism cooperating with the operating mechanism to trip open the separable contacts, the tri mechanism comprising; a current sensor structured to sense a value of current flowing through the separable contacts, a circuit structured to receive first frequency pulses having a number of first frequencies from a conductor in series with the separable contacts, a transmitter structured, to transmit second frequency pulses having a second frequency to the conductor, the second frequency being di fferent than the number of first frequencies, and a processor comprising a routine structured to input the sensed value of current from the current sensor, determine if the sensed value of curren t exceeds a predetermined value and responsively cause the transmitter to transmit the second frequency pulses having the second frequency to the conductor,, monitor within a predetermined lime after determining that the sensed value of current exceeds the -predetermined value if a number of the first frequency pulses having the number of first frequencies is received by the circuit from the conductor, and responsively delay otitputting a trip signal, and, otherwise, immediately output the _. trip signal, wherein each corresponding one of the number of first electrical switching appara tus is structured to transmit the second frequency pulses having a same second frequency to the conductor of the

corresponding one of the number of first, electrical switching apparatus, wherein each corresponding one of the number of second electrical switching apparatus is structured to transmit the second frequency pulses having a same second frequency to the conductor of the corresponding one of the number of second electrical switching apparatus, and wherein the same second requency of the corresponding o e of the number of first electrical s witching apparatus is different than the same second frequency of the corresponding one of the number of second electrical switching apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the disclosed concep t can he gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

Figure I is a block diagram of a system in accordance with embodiments of the disclosed concept.

Figure 2 is a block diagram of a circuit breaker trip unit in accordance with another embodiment of the disclosed concept,

Figure 3 is a -flowchart of a routine of the processor of Figure 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As employed herein, the term "number" shall mean one or an integer greater than one {i.e., a plurality).

As employed herein, the term "processor" shall mean a programmable analog and/or digital device thai can store, retrieve, and process data; a computer; workstation; a personal computer; a microprocessor; a microcontroller; a

microcomputer; a digital signal processor (DSP); a central processing unit; a maiwframe computer; a rami -computer: a server; a networked processor: or any suitable processing device or apparatus.

As employed herein, the term "electrical conductor" shall mean a wire (e.g., solid; stranded; insulated; non-insulated), a copper conductor, an aluminum conductor, a suitable metal conductor, or other suitable material or object that permits an electric current to flow easily.

As employed herein, the statement that two or more parts are

"connected" or "coupled" together shall mean that the parts ai¾ joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are "attached" shall mean that the parts are joined together directly.

The disclosed concept is described, in. association with single-pole circuit breakers, although the disclosed concept is applicable to a wide range of electrical switching apparatus having any suitable number of poles,

Figure I shows a system 2 including a first branch level 4 having a number of first electrical switching apparatus 6 (only one example circuit breaker 6 is shown) and a second branch level 8 downstream of the first branch level 4 and having a number of second electrical switching apparatus 10 (four example circuit breakers 10 are shown). As is conventional, as shown with the example circuit breaker 6, each of the number of first electrical switching apparatus 6 and the number of second electrical switching apparatus 10 includes separable contacts 12, an operating mechanism 14 structured to open and close the separable contacts 12, and a trip mechanism 16 cooperating with, the operating mechanism 14 to trip open the separable contacts 12.

Also referring to Figure 2, in accordance with aspects of the disclosed concept, the circuit breaker trip mechanism 1 includes a current sensor 1.8 structured to sense a value 1 of current 20 flowing through the separable contacts 12, a circuit 22 structured to receive frequency pulses 24 ha ving a number of frequencies (fV) from an electrical conductor 26 in serie with the separable contacts 12, a transmitter 28 structured to transmit frequency pulses 30 having a fre uency (fj) different than the number of frequencies (f ) to the conduc tor 26, and a processor, such as the example microprocessor ίμ,Ρ) 32 including a routine 34 (Figure 3). The trip mechanism 1 provides an autonomous short circuit zone location detection trip circuit. The current sensor 18 is preferably a 50 Hz 160 Hz circuit thai monitors the value 19 of the current 20 flowing through the separable contacts 12, The transmitter 28 is preferably a high frequency pulse generator that generates a series of high frequency pulses at frequency (fV) and at rate (Mf). The circuit 22 is preferably a high frequency current monitoring circuit that monitors a high frequency current corresponding to a. series of the high frequency pulses 24 at frequency (f ) and at rate (Ms) originating from one of the number of second electrical switching apparatus 10. Frequencies and i¾ can be any suitably different frequencies, and. rates Mj and M ₂ can be any suitably different rates.

The routine 34 of Figure 3 is structured to input the sensed value (1) of current .1 from the current sensor 18 of Figure 2, determine if the sensed value (!) of current 19 exceeds a predetermined value (e.g., i ^' tX and responsively cause the transmitter 28 to transmit the frequency pulses 30 having the different frequency (fj) to the conductor 26. monitor within a predetermined time (T) after determining thai the sensed value (I) of current. 19 exceeds the predetermined value (e.g., ί·. } if a number of the frequency pulses 24 having the number of frequencies (¾} is received by the circuit 22 from the conductor 26, and responsiveiy delay outputting a trip signal 36, and, otherwise, immediately output the trip signal 36. As is conventional, the trip signal 36, when output., energizes a circuit breaker trip coil 35, which causes the operatin mechanism 14 to trip open the separable contacts 12. The

predetermined value, ! _¾ , is a value that is equal to the rated current value of the circuit breaker 6.

Each corresponding one of the number of first electncal switching apparatus 6 of Figure 1 is structured to transmit the second frequency pulses 30 of Figure 2 having a same second frequency to the conductor 26 of the corresponding one of the number of first electrical switching apparatus 6. Each corresponding one of the number of second electrical switching apparatus 10 is structured to transmit the second frequency pulses 30 having a same second frequency to the conductor 26 of the corresponding one of the number of second electrical switching apparatus 10. The same second frequency of tiie corresponding one of the number of first electrical swi tchiag apparatus 6 is different than the same second frequency of (he

corresponding one of the number of second electrical switching apparatus 0.

Electrical switching apparatus 10 in the same branch level, such as 8, will generate the same high frequency pulses, such as 24, but different from the high frequency pulses, such as 30, from electrical switching apparatus 6 in different branch levels, such as 4. As will be described in greater detail, below, hi connection with Figure 3, upon detection of a current exceeding die predetermined value (e.g., k), an electronic trip unit 38 of the electrical switching apparatus 6 will send the high frequency pulses 3 and also monitor within the predetermined time period (T) if there are high frequency pulses 24 coming from the electrical switching apparatus 10 in the next branch level 8 downstream. If not, the electrical switching apparatus 6 will trip immediately: Otherwise, the electronic trip unit 38 will switch its trip curve 39 (Figure 2) to a delayed trip in order that the corresponding downstream electrical switching apparatus 10 can clear the fault 37 (Figure 1). The trip curve 39 can be one of various trip curves and characteristics 41. For example, the routine 34 (Figure 3) is structured to provide a number of short delay, long delay and instantaneous trip functions.

For example, the electronic trip unit 38 includes a first setting (fj) of what frequency of pulses 30 to send and a second setting (¾) of what .frequency of pulses 24 come from the next branch level (e.g., 8) downstream. Hence, that electronic trip unit 38 would ignore different frequency pulses 40 (shown in phantom line drawing in Figure 1 ) from upstream branch levels, such as 42 (shown in phantom line drawing in Figure 1 ), or other different frequency pulses 4 (shown in phantom, line drawing in Figure I) from still lower downstream branch levels, such as 46. Since the fault 37 is upstream of the electrical switching apparatus 48 of the lower downstream branch level 46, no action is needed by thai apparatus.

if the electrical switching apparatus 48 is the lowest branch circuit level, as determined at 63 of Figure 3, upon detection of a current exceeding the predetermined value (e.g., 1 _¾ ) at 58, the electronic trip unit 38 of the electrical switching apparatus will send high frequency pulses 30 at 61 and the electronic trip unit 38 will trip the electrical switching apparatus 48 at 65 according to the trip curve 39 (Figure 2) io clear the fault downstream of the electrical switching apparatus 48. The trip curve 39 can be one of various trip curves and characteristics 4 . For example, the routine 34 (Figure 3) is structured to provide a number ^' of short delay, long delay and instantaneous trip functions.

The example uP 32 of Figure 2 includes a storage component, such as memory 50, having a number (e.g., one) of values 52 defining the number (e.g., one) of received frequencies (£>), and another value 54 defining the transmitted frequency (ft).

Referring to Figure 3, the routine 34 detetmines whether the trip signal 36 of Figure 2 is delayed or output immediately. At 56, the routine 34 monitors the 50 Hz / 60 Hz current (I) from the circuit 18 of Figure 2. Next, at 58, if the current (I) is not greater than the predeterniined value (I») _» then no trip is actuated at 60. On the other hand, if the current (J) is greater than the predetermined value (ft), then two steps are taken. At 61 , the pulse generator 28 is acti vated to generate the series of high frequency pulses 30 at frequenc (ft) and rate (Mi), Also, at 63, it is determined if the circuit breaker is the lowest branch level If so, then execution resumes at 65. Otherwise, at 62, using the circuit 22 of Figure 2, high frequency pulses 24 are monitored at irequency (¾) and rate (M ₂ ) by sensing current (½). Next, at 64, it is determined if the sensed current (Ιβ) is greater than a predetermined value {¾) and if the measured time (Δίβ) between pulses is equal to 1 M? within a predetermined time period T. if so, then at 66, a delayed trip allows the downstream, circui t breaker (e.g., circuit breaker 10 of branch level 8 of Figure 1) to clear the fault, if not, then an instantaneous trip is actuated at 68 to clear the fault 37.

Each circuit breaker frame has its own frequency {„ and pulse rate M». Here, ft and Mj define the high frequency pulses for the downstream circuit breaker, and ft and M ₅ define the high frequency pulses for the upstream circuit breaker.

Circuit breakers on the same level (e.g.. intermediate level: lowest level) use the same frequency and the same pulse rate. ^" There is only one circuit breaker at the highest or top level. The high frequency current I¾ can be monitored by employing a suitable high frequency current sensor (e.g., without limitation, a current transformer (GT)) of the circuit breaker electronic trip unit 8. The example high frequency current sensor CT is tuned to a specific high frequency. Hence, the example top level circuit breaker 6 only monitors the high frequency signal(s) from the intermediate circuit breakers 10. The high frequency current In is the high frequency current caused by the pulse train of the f? / Μ-χ defined high frequency pulses from the intermediate circuit breakers 10. The example top level circuit breaker 6 only transmits the local frequency ¾ and only receives the immediaie downstream frequency f>, but not a lower level frequency f ₃ . The predetermined values I _} and 1. ₂ are known by the top level circuit breaker 6.

Example

As a .non-iirahing example for Figure 3, the current I. is 250 A, the predetermined value lj is 250 A (rated current), the frequency f is 1.5 MHz, the rate Mi is 25 mS, the frequency f> is 1 MHz, the rate Mj is 20/m.S, the predetermined value I ₂ is 1 mA, and the time T is 500 pS. The predetermined time T corresponds to a predetermined count ofihe frequency pulses at frequency fj Tepeaied at the rate Mj. In this example, the predetermined count is ten (e.g., 1 x i/(20/mS) - lO 50 μ$ - 500 uS >.

While specific embodiments of the disclosed concept have been described in detail, it will be -appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be gi ven the full breadth of th claims appended and any and all equivalents thereof.