J
Can an extremely high demand of power lower the bus voltage on a nationwide grid?
Thanks
Thanks
Of course it will if the demand is greater than the available grid capacity available. I live in the Philippines and they use the word "brownouts" here because, when the voltage reduces, the old fashioned incandescent light bulbs turned a kind of brown color. Many places with unstable grids experience these kind of problems when demand gets high, voltage and frequency will drop and they will usually then need to implement a program of rotating power outages to save the grid from collapse.
J
job2004
Great I appreciate it. Would you elaborate on how technically the frequency and voltage drop? I am in rental power operations but not at the technical level.
job2004,
When we're talking about electrical power--<b>real power</b>: watts; kW, MW--we're basically referring to current. [NOTE: I'm not talking about the effects of reactive current--VArs--on the system, which is another contributor to grid problems when load is high. This description is only referring to what happens to the real power, the (I^2*R) component of electrical power transmission and distribution. Power is also equal to (V*I) when we ignore reactive power, which is another way to say (I^2*R), and if voltage is held relatively constant as it usually is on most grids then power transmission is proportional to current. The only reason I'm introducing any formulae into the discussion is to show the effects of V (Voltage) and I (current) on real power. And these are the simplest formulae in the power world, simple multiplication without vectors and geometry.]
Current is what "flows" on an electrical power transmission and distribution system; voltage is what "pushes" current to flow. Current does the work; voltage is the force "behind" the current; without both, no work will be done. When the load on an electric motor increases, so does the current. Under normal conditions the voltage of the applied electrical power essentially remains the same, but as the load on a motor changes the current changes. More load, more current; less load, less current.
Every electrical conductor (wire; cable; bus bar; etc.) has resistance associated with it, and for that reason there is a voltage developed in (across) every conductor that current flows through. This voltage that is developed as a result of current flowing through it detracts from the applied voltage, lowering the voltage at the other end of the conductor. The longer the conductor the greater the resistance, and the greater the resulting voltage drop from one end of the conductor to the other end.
It is precisely this reason that AC power systems came into being (as opposed to DC power systems for general electrical power generation, transmission and distribution)--because with AC the voltage (and current) levels can be very easily 'transformed' (using induction transformers). By raising the voltage level, the resulting current decreases proportionally. So, by transforming the voltage of power being transmitted long distances the resulting current flows will be reduced, reducing the voltage drops in the transmission and distribution conductors (wires and cables). More power (current) can be transmitted over long conductors by raising the voltage thereby reducing the current and reducing the resultant voltage drop through the conductors. The alternative would be to use extremely large conductors (cross-sectional area) to transmit the electrical power, but that would greatly increase cost and they would be extremely heavy as well.
Something that is also very important happens when current flows through a conductor (and the wires of an electric transmission and distribution system are just that--conductors): heat is generated (due to the resistance of the conductor). The temperature of a conductor also affects the resistance of the conductor, and as the temperature of a conductor increases so does the resistance. As the resistance increases the voltage drop in the conductor (sometimes referred to as "across the conductor") increases.
It is this voltage drop because of resistance increases due to temperature rise caused by high current flow that is one of the primary causes for the grid voltage to sag when power demand is high--it is not the only cause, but one of the largest contributing factors to grid voltage drop on high demand (load). If the grid transmission and distribution system isn't properly sized to accommodate the expected maximum power flow(s) then abnormal voltage drops in the conductors occur which contribute immensely to low grid voltage.
Voltage is the "pressure" which causes current to flow or to remain flowing. Without "pressure" current doesn't flow as well. It's a nasty downward spiral if not properly addressed by grid operators/supervisors.
And, remember, electrical power is just the means for converting torque to amperes that can be transmitted and distributed over long distances and then reconverted into torque or useful work at the other end of the circuit(s). A former colleague of mine used to quote one of his university professors when we were talking about power and people confused voltage with current: "Voltage doesn't do anything unless you put it in a Volkswagen and push the Volkswagen down the street." The implication was that current does the work--there has to be a circuit for current to flow for work to be done; voltage by itself does nothing. Voltage just provides the "pressure." Pressure is very important, but voltage isn't what does the work. Again, voltage is usually relative constant under normal circumstances and it's current flow that varies as work is done.
Hopefully other contributors can talk about the reactive component of high grid demand (without maths and vectors and questions).
As for why the frequency drops, an AC electrical system can be compared to a bicycle carrying packages which has to travel at a specific speed (AC electrical systems are supposed to operate at a specific frequency--and the speed of the generator rotor and the generator prime mover and frequency are directly related). If the bicycle rider is producing, say, 95% of his available power to keep the bicycle and packages moving at the desired speed and more packages are added to the bicycle such that the power required from the rider is more than 100% of his capability then the bicycle and packages will slow down.
The exact same thing happens to an electrical grid when the load (demand) exceeds the generation capacity--the ability of the generator prime movers to supply torque to the generator rotors: the grid frequency will start to decrease.
The purpose of an electrical system is to transmit torque over wires from one place (where the generator and its prime mover is located) to many different places where torque is required (for pumping water, for powering lights, for air conditioning systems, for computers and computer monitors, and for televisions, etc.). No one ever seems to have a problem with understanding that motors convert amperes into torque to drive pumps and compressors and fans and elevators and such--but they struggle with the concept that generators convert torque into amperes. The electric motors aren't actually doing the work of driving pumps and compressors and fans and elevators--the prime movers driving the generators are really doing the work.
On an AC electrical system, the power has to be produced and transmitted at a particular frequency (so that transformers will work properly--and since that's how AC motors are designed to operate at specific speeds, as well, since speed and frequency are directly related at the motor end of the circuit just like they are at the generator end of the circuit). And when the load exceeds the ability of the system to maintain rated frequency then the inertia of the system starts to drop to provide the required power--but at a lower frequency--until such time as more generator prime movers can be started and synchronized to the system.
Hope this helps!
When we're talking about electrical power--<b>real power</b>: watts; kW, MW--we're basically referring to current. [NOTE: I'm not talking about the effects of reactive current--VArs--on the system, which is another contributor to grid problems when load is high. This description is only referring to what happens to the real power, the (I^2*R) component of electrical power transmission and distribution. Power is also equal to (V*I) when we ignore reactive power, which is another way to say (I^2*R), and if voltage is held relatively constant as it usually is on most grids then power transmission is proportional to current. The only reason I'm introducing any formulae into the discussion is to show the effects of V (Voltage) and I (current) on real power. And these are the simplest formulae in the power world, simple multiplication without vectors and geometry.]
Current is what "flows" on an electrical power transmission and distribution system; voltage is what "pushes" current to flow. Current does the work; voltage is the force "behind" the current; without both, no work will be done. When the load on an electric motor increases, so does the current. Under normal conditions the voltage of the applied electrical power essentially remains the same, but as the load on a motor changes the current changes. More load, more current; less load, less current.
Every electrical conductor (wire; cable; bus bar; etc.) has resistance associated with it, and for that reason there is a voltage developed in (across) every conductor that current flows through. This voltage that is developed as a result of current flowing through it detracts from the applied voltage, lowering the voltage at the other end of the conductor. The longer the conductor the greater the resistance, and the greater the resulting voltage drop from one end of the conductor to the other end.
It is precisely this reason that AC power systems came into being (as opposed to DC power systems for general electrical power generation, transmission and distribution)--because with AC the voltage (and current) levels can be very easily 'transformed' (using induction transformers). By raising the voltage level, the resulting current decreases proportionally. So, by transforming the voltage of power being transmitted long distances the resulting current flows will be reduced, reducing the voltage drops in the transmission and distribution conductors (wires and cables). More power (current) can be transmitted over long conductors by raising the voltage thereby reducing the current and reducing the resultant voltage drop through the conductors. The alternative would be to use extremely large conductors (cross-sectional area) to transmit the electrical power, but that would greatly increase cost and they would be extremely heavy as well.
Something that is also very important happens when current flows through a conductor (and the wires of an electric transmission and distribution system are just that--conductors): heat is generated (due to the resistance of the conductor). The temperature of a conductor also affects the resistance of the conductor, and as the temperature of a conductor increases so does the resistance. As the resistance increases the voltage drop in the conductor (sometimes referred to as "across the conductor") increases.
It is this voltage drop because of resistance increases due to temperature rise caused by high current flow that is one of the primary causes for the grid voltage to sag when power demand is high--it is not the only cause, but one of the largest contributing factors to grid voltage drop on high demand (load). If the grid transmission and distribution system isn't properly sized to accommodate the expected maximum power flow(s) then abnormal voltage drops in the conductors occur which contribute immensely to low grid voltage.
Voltage is the "pressure" which causes current to flow or to remain flowing. Without "pressure" current doesn't flow as well. It's a nasty downward spiral if not properly addressed by grid operators/supervisors.
And, remember, electrical power is just the means for converting torque to amperes that can be transmitted and distributed over long distances and then reconverted into torque or useful work at the other end of the circuit(s). A former colleague of mine used to quote one of his university professors when we were talking about power and people confused voltage with current: "Voltage doesn't do anything unless you put it in a Volkswagen and push the Volkswagen down the street." The implication was that current does the work--there has to be a circuit for current to flow for work to be done; voltage by itself does nothing. Voltage just provides the "pressure." Pressure is very important, but voltage isn't what does the work. Again, voltage is usually relative constant under normal circumstances and it's current flow that varies as work is done.
Hopefully other contributors can talk about the reactive component of high grid demand (without maths and vectors and questions).
As for why the frequency drops, an AC electrical system can be compared to a bicycle carrying packages which has to travel at a specific speed (AC electrical systems are supposed to operate at a specific frequency--and the speed of the generator rotor and the generator prime mover and frequency are directly related). If the bicycle rider is producing, say, 95% of his available power to keep the bicycle and packages moving at the desired speed and more packages are added to the bicycle such that the power required from the rider is more than 100% of his capability then the bicycle and packages will slow down.
The exact same thing happens to an electrical grid when the load (demand) exceeds the generation capacity--the ability of the generator prime movers to supply torque to the generator rotors: the grid frequency will start to decrease.
The purpose of an electrical system is to transmit torque over wires from one place (where the generator and its prime mover is located) to many different places where torque is required (for pumping water, for powering lights, for air conditioning systems, for computers and computer monitors, and for televisions, etc.). No one ever seems to have a problem with understanding that motors convert amperes into torque to drive pumps and compressors and fans and elevators and such--but they struggle with the concept that generators convert torque into amperes. The electric motors aren't actually doing the work of driving pumps and compressors and fans and elevators--the prime movers driving the generators are really doing the work.
On an AC electrical system, the power has to be produced and transmitted at a particular frequency (so that transformers will work properly--and since that's how AC motors are designed to operate at specific speeds, as well, since speed and frequency are directly related at the motor end of the circuit just like they are at the generator end of the circuit). And when the load exceeds the ability of the system to maintain rated frequency then the inertia of the system starts to drop to provide the required power--but at a lower frequency--until such time as more generator prime movers can be started and synchronized to the system.
Hope this helps!
J
job2004
Thank you Very much. Greatly appreciate it.
J
job2004
This is a 50 mw diesel rental power. Our kits lay out is: Every 6 generators feed into one transformer (Actually they are 2 transformers in one compartment), 3 switchgears, and 3 step up transformers which feed into client's switchgear.
Would you please explain how all these kits are connected?
Thanks
Would you please explain how all these kits are connected?
Thanks
J
job
Would someone please give some basic information?
Thanks
Thanks
