RS PRO 1365377 LED Digital Panel Multi-Function Meter 3-Digit 3 Line Onsite Programmable
Mfr. Part #: 1365377 / RS Stock #: 71768520

Current, Frequency, On Hour, RPM, Run Hour, Voltage

https://assets.alliedelec.com/v1563876034/Datasheets/b8fb981a1bddc68b50b1f928b5c35823.pdf

$75

Generators and emergency power systems are essential to enabling hospitals and health care facilities to effectively serve their communities //

NFPA 70: National Electrical Code requires every hospital to have two independent power sources that provide a minimum level of reliability: a normal source (i.e., utility) and an alternate source (i.e., generator, fuel cell system or battery system).

Because most health care facilities have traditionally used generators as their alternate source due to runtime and maintenance advantages, this article will focus on generators and essential electrical system (i.e., “emergency power”) design.

For the purposes of this article, the NEC Article 517 term “essential electrical system” and Article 700 term “emergency power system” are synonymous because emergency systems are defined in NEC Article 700, which is applied specifically to hospitals in NEC Article 517.

An emergency system is defined by the NEC as “those systems legally required and classed as emergency by municipal, state, federal and other codes.”

NFPA 110: Standard for Emergency and Standby Power Systems defines the various components that makeup an emergency power system and comprises the emergency power supply and emergency power supply systems.

The EPS is the alternate power source, which in this case is the generator(s). The EPSS consists of the conductors, distribution equipment, overcurrent protective devices, transfer switches and all control, supervisory and support equipment needed for the system to operate between the generator and the transfer switch. Conductors, distribution equipment and overcurrent protective devices on the load side of the transfer switches are not considered part of the EPSS per NFPA 110, but are considered part of the overall emergency power system (see Figure 1).

Meter forms 3, 4, 5, 6, 8, 9

Electrical and other engineers should understand basic features when selecting, specifying and applying electrical distribution systems. To narrow the broad scope of electrical distribution, this discussion will focus on practical considerations for specifying electrical distribution systems.

This information will focus on common low-voltage 480/120-volt electrical distribution equipment encountered in many types of facilities and will touch on medium-voltage equipment. Also, basic considerations for rooms housing these pieces of electrical equipment will be highlighted.

Learning objectives:

• Understand basic features when selecting and specifying electrical distribution equipment.
• Know the types of overcurrent protection devices (molded case circuit breakers, insulated case circuit breakers, low-voltage power circuit breakers and fuses.
• Learn about switchboards as outlined in UL 891 and switchgear as outlined in UL 1558.
• Learn about panelboards, transformers and other electrical equipment.
• Understand basic room and space requirements for the electrical equipment.

Figure 1. This animation of a simple 3-phase power system shows the basic principle of a balanced load. Note how the particles' of current entering and leaving the star node sum to zero. Source: BillC at Wikimedia.

It should be clear that we could connect the star point of the generator to the star point of the load with a neutral conductor but that no current would flow in it as the three phases are perfectly balanced.

Figure 2. Taking the OP's diagram to represent the currents in the balanced load we can see that at examples (1), (2) and (3) that they sum to zero. (I didn't cheat by stretching and of the arrows in each set.)

If we unbalance the load things change somewhat. Without a neutral the star points will shift to adjust the phase-star voltage to maintain the current balance.
If we add the neutral then we can force the star points to remain at the same potential and maintain the same voltage on each load phase despite the different currents in each. The difference between the phase currents must be carried by the neutral.

Why not three lines all in the same phase?

1. Because then there is no return path.
2. Because single phase has no "rotation". Three phase makes it very simple to make a rotating motor with phase sequence determining the direction of rotation. Swap two phases and the direction is reversed.

Is there less loss when the phases of the three lines are all different?

1. Three phase power distribution requires less copper or aluminium for transferring the same amount of power as compared to single phase power.
2. The size of a three phase motor is smaller than that of a single phase motor of the same rating.
3. Three phase motors are self starting as they can produce a rotating magnetic field. The single phase motor requires a special starting winding as it produces only a pulsating magnetic field.
4. In single phase motors, the power transferred in motors is a function of the instantaneous power which is constantly varying. In three-phase the instantaneous power is constant.
5. Single phase motors are more prone to vibrations. In three phase motors, however, the power transferred is uniform through out the cycle and hence vibrations are greatly reduced.
6. Three phase motors have better power factor regulation.
7. Three phase enables efficient DC rectification with low ripple.
8. Generators also benefit by presenting a constant mechanical load through the full revolution, thus maximising power and also minimising vibration.

I'll focus my answer on transmission alone, without explaining why 3 phase is useful in general because other answers did that.

Transmission of power is a compromise. A compromise between transmission efficiency and ease of conversion. The most efficient way of transmitting electric power is DC. This is why most superlong lines are HVDC (high voltage direct current). However, DC is the worst for converting it to HV when you want to send it from power station, and back to LV when you want to feed it to consumers.

AC on the other hand is very convenient to convert - just put a transformer. However the transmission sucks. Eg. AC radiates some of the energy away, but that's not the main concern. If you look at sinusoidal graph, you'll realize that AC wire doesn't actually work 100% of the time. While DC cable carries useful current all the time (one can think of DC as 100% duty cycle PWM), AC cable carries current only part of the time. This means that for the same peak voltage (which dictates cost of insulating the line) and for the same peak current (which dictates size and cost of conductors), AC can transmit only part of the power.

Here comes the idea of multi-phase. Of course multi-phase alone doesn't mean a thing, you can have 3 phases on 6 conductors (3 pairs completely independent of each other). The key here is sharing of the wires between phases. It's like a hot bunk on a warship - 2 seamen share 1 bunk, when one guy awakes and starts his shift, the other ends his shift and goes to sleep. The point is to not have an empty bunk just wasting space, and 3-phase AC works on the same concept: in the time when one phase "rests", another phase is re-using one of it's wires to transmit own current. It's not clear at first sight because it's very fluid, one falling towards 0 while the others rise, and there never is a time when one phase as a wire all to itself. But the point is to re-use the idle time of the wires.

Why 3? Because 2 is too small, you can't have 2 phases on 2 wires. 3 is the minimum number of phases that can share all the wires. Why offset? Because one phase on X conductors is same thing as 1 conductor X times thicker.

When you compare the 3 phase system to a 1 phase system, you can clearly see that with adding just 50% more wires you get 3 times more current.

3-phase transmission uses the wires TWICE as effectively as 1-phase. So you can use half as much copper when building the line.

A variable-frequency transformer is a doubly fed electric machine resembling a vertical shaft hydroelectric generator with a three-phase wound rotor, connected by slip rings to one external power circuit. The stator is connected to the other. With no applied torque, the shaft rotates due to the difference in frequency between the networks connected to the rotor and stator. A direct-current torque motor is mounted on the same shaft; changing the direction of torque applied to the shaft changes the direction of power flow.

The variable-frequency transformer behaves as a continuously adjustable phase-shifting transformer. It allows control of the power flow between two networks. Unlike power electronics solutions such as back-to-back HVDC, the variable frequency transformer does not demand harmonic filters and reactive power compensation. Limitations of the concept are the current-carrying capacity of the slip rings for the rotor winding.

RCDs are very effective devices to provide protection against fire risk[1] due to insulation fault because they can detect leakage currents (ex : 300 mA) which are too low for the other protections, but sufficient to cause a fire. //

Some tests have shown that even a fault current as low as 300 mA can induce a real risk of fire (see Figure F74) //

For TT, IT and TN-S systems the use of 300 mA sensitivity RCDs provides a good protection against fire risk due to this type of fault. //

The IEC 60364-4-42:2010 (clause 422.3.9) makes it mandatory to install RCDs of sensitivity ≤ 300 mA in high fire-risk locations (locations with risks of fire due to the nature of processed or stored materials - BE2 condition described in Table 51A of IEC 60364-5-51:2005). TN-C arrangement is also excluded and TN-S must be adopted. //

In TN-C system, RCD protection cannot be used, as the measurement of earth fault current by a sensor around line conductors and PEN will lead to permanent wrong measurement and unwanted trip. But a protection less sensitive than RCD but more sensitive than conductors’ overcurrent protection can be proposed. In North America this protection is commonly used and known as “Ground Fault Protection”.

Have you ever wondered why the square root of three shows up in so many three-phase power calculations?

Where does this number come from, and why is it so special?

While the long answer to these questions comes from trigonometry, the good news is that we can use phasor diagrams to make explaining it very simple to understand.

Understanding phasor diagrams is an important skill for relay testing and working through the examples in this article will give you a much deeper understanding of and appreciation for the phasor quantities in phasor diagrams. Regardless of which part of the industry you work in, this will greatly benefit your career in electrical power and relay testing.

The following chart includes the values generated for a three-phase balanced offline-meter test into an SEL-351 relay using a Megger Test-Set or RTS.

Test-Set
Relay Magnitude Angle
Voltage Channel V1 VA 69.28V 0°
Voltage Channel V2 VB 69.28V 120°
Voltage Channel V3 VC 69.28V 240°
Current Channel I1 IA 1.000A 0°
Current Channel I2 IB 1.000A 120°
Current Channel I3 IC 1.000A 240°

The relay is connected to 300:5 CTs and 35:1 PTs. Is everything correct in the following meter test?

Here’s what we know so far:

• The metering results aren’t zero, which means the relay’s analog to digital converters are working.
• The CT and PT ratio settings in the relay are correct (notice that we don’t need to look at the actual settings to determine this). We’re injecting 1A in all three phases and the relay is reporting approximately 60A. The worst-case accuracy is -0.355% error, which is consistent with the 60:1 CT ratio. The relay is reporting approximately 2.42kV in all three-phases with a maximum percent error of -.07%, which matches the PT ratio.
  • The relay is looking in the correct direction because the currents and voltages are in-phase.
  • We are injecting A-B-C, or 1-2-3, rotation because the following pattern exists in the relay and test-set: A-Phase is 0°, B-Phase lags A-Phase by 120°, and C-Phase lags A-Phase by 240°.
  • The relay is programmed with the WRONG phase rotation because the sequence components show 0% positive sequence, 100% negative sequence, and 0% zero-sequence.

Understanding phase rotation is vital when connecting two systems together because the results can be catastrophic if someone doesn’t understand how to interpret phase rotation drawings. You would think something as important as phase rotation would have consistent terms across the entire industry. Unfortunately, you’d be wrong. //

You can’t determine phase rotation with a phasor diagram unless you know the one universal rule in the relay testing world. ALL PHASORS ROTATE COUNTER-CLOCKWISE. //

If you want to be sure you understand phase rotation correctly, put your finger anywhere on the phasor diagram and imagine that the phasors are spinning counter-clockwise. Start paying attention when your reference phasor crosses your finger. Which phasor crosses your finger next? Which is the last phasor to cross your finger?

If you’ve read anything about relay testing written in the last ten years or so, you’ll see a pattern; No-one is talking about the traditional pickup and timing tests most relay testers (and most automated relay testing software) use to test relays. You are much more likely to read terms like “dynamic testing” or “system testing”, which are the true future of relay testing. Unfortunately, these terms aren’t well defined and are usually embedded in a short article written in engineer-ese that even I, a relay testing “expert”, usually have trouble following.

In 2014, the National Electrical Code included a new requirement. 690.12(1) through (5) A short requirement, only six sentences.

PV system circuits installed on or in buildings shall include a rapid shutdown function that controls specific conductors in accordance with 690.12(1) through (5) as follows.

1. More than 5’ inside a building, or more than 10’ from a PV array
2. Controlled conductors shall be limited to not more than 30V and 240 volt-amperes within 10 seconds of rapid shutdown initiation.
3. Voltage and power shall be measured between any two conductors and between any conductor and ground.
4. The rapid shutdown initiation methods shall be labeled in accordance with 690.56(B).
5. Equipment that performs the rapid shutdown shall be listed and identified.

But those six short sentences had a big change on PV system design. Gone were the days of simply wiring the solar panels, or modules, to the grid tied inverter or charge controller through a simple pass-thru or combiner box. Rapid ShutDown (RSD) has a noble cause. It is to protect the firefighters trying to put out a fire in your home or business. Even when they turned off the grid power to your house, and the inverter automatically shut itself off (in accordance with UL1741), the wires from the solar array all the way down into the inverter or controller were still live. In grid tied systems, they could have as much as 600VDC. Combine that voltage with a firefighter’s ax to vent the roof, and you have a disaster on your hands.

Rapid Shutdown gives the firefighters a way to also shut down the DC power from the solar array to the inverter. In 2014, it could shut it down to the area up to 10’ from the solar array, and more than 5’ of entering a building.

LATEST NEWS
LERC’s BoC Reacts to Massive Load Shedding

The Board of Commissioners (BoC) of the Liberia Electricity Regulatory Commission (LERC) has described the Liberia Electricity Corporation’s (LEC) massive load shedding in its operational areas as unacceptable and calls on LEC Management to set into motion remedies to address the electricity generation nightmare.

This load shedding being carried out by LEC as observed is in violation of the minimum service levels in Schedule Two (2) of the Customer Service and Quality of Supply Regulations (CSQOSR), which ensures that duration of outages cannot exceed eight hours and therefore the commission directs LEC to take urgent steps to curtail these load shedding.

LERC recalls that during LEC tariff application review process, the Commission, on numerous occasions, expressed concerns about the seasonal variations impacting Mount Coffee power generation capacity especially during the Dry Season, to which LEC assured the LERC that effective January 2022, it would have sufficient fuel stock to generate 29.4 MW from the Bushrod Thermal Plant complemented by power imports via the Transco-CLSG arrangements during the Dry Season.

The LERC considers LEC’s action as a complete disregard of the Commission’s regulatory authority and reminds LEC of the necessary actions at the Regulator’s disposal consistent with the 2015 Electricity Law of Liberia and applicable regulations.

MONROVIA – Members of the regional parliament attending the ECOWAS Fifth Legislative Parliamentary Seminar and 2022 Extraordinary Session of the ECOWAS Parliament were forced to call off the session on Thursday due to the sudden breakdown of the generator supplying the Ministerial Complex electricity.

The sudden blackout, FrontPageAfrica gathered, left some of the dignitaries stranded in the elevator at the Ministerial Complex. They were rescued by technicians at the building.

“The generator broke down, but these things happen just like how humans fall and die. It started with the fuel – the machine ran out of fuel and they managed to get fuel, they tried putting it and it will come on and go off. They tried it several times it did not come on. Some of the dignitaries were stuck in the lift and the technicians had to come to their rescue,” a technician, preferring anonymity, working on the scene of blackout at Ministerial Complex Thursday.

The power was later restored but the Parliamentarians said they were not comfortable there any longer and would rather prefer using the Monrovia City Hall for the rest of their sessions until Monday when the heads of states are in.

“They were called back but they said they will rather use City Hall on Friday because they do not want to have a repeat. They asked the technicians to work on the machines to ensure that it does not happen when the heads of states are having their meeting next Monday,” a FrontPageAfrica reporter covering the session said.

After over 60 years of service, the James River Power Station (JRPS) is officially being retired. The decision to retire JRPS was based on escalating costs for compliance upgrades, aging infrastructure, and the availability of reliable renewable resources.

To decommission the power station, steps will be taken to dismantle or demolish parts of the plant. This work will include some exterior components, the lakeside water intake structure, and removal of the four stacks.

The demolition process will be handled under strict safety and environmental compliance rules. The process will begin mid-September and is expected to conclude in early 2022. Usable areas of the facility, such as the building office space, electrical substation equipment, and two natural gas combustion turbines will remain.

This table lists the minimum sizes of grounding conductors for grounding raceways and equipment.

The last fixed-price government contracts offered for offshore wind energy in Britain—hardly the cheapest of renewables—were under 5p per kilowatt hour (kWh). That’s less than a quarter of the typical domestic tariff (what most people pay for electricity at home) that consumers are set to face in 2022. Households are paying for their electricity several times what it now costs to generate and transmit it from the cleanest energy sources at scale.

The design of electricity systems has failed to catch up with the revolution in renewable energy. Competitive electricity markets, established in many countries to try to minimize costs, are actually suffering the greatest price rises. This is not because governments elsewhere use taxes to subsidize electricity (though some do), but because in wholesale electricity markets, the most expensive generator sets the price.

Since renewables and nuclear will always run when they can, it is fossil fuels—and at present, unequivocally gas, plus the cost of taxes on CO₂ pollution—that set the price almost all the time, because some gas plants are needed most of the time, and they won’t operate unless the electricity price is high enough to cover their operating cost. It’s a bit like having to pay the peak-period price for every train journey you take.