This is a clarification to a series of emails I am having with an individual that seems to be confused with Phasors, Rotation and Reference Points. First let me discuss phase rotation. Imagine I was looking at a rotating wheel that was moving counterclockwise as in the picture below. What would I see? I would […]
Question From Inbox: Max Power Sent and Loading
Question from inbox: In problem 34 of Vol II, I am having trouble understanding the answer given. I understand that if the sending angle is greater than the receiving angle then real power flows from the sending end to the receiving end. I am having trouble understanding in regards to max power and load admittance. […]
Question From Inbox: Sizing Neutral Resistor
Question from inbox: This question is for problem 7 on page 96 of the Cram for the PE guide. The problem deals with a 150 MVA generator connected to a 13.8 kV bus. I think this is a very good problem, but I am having trouble getting the same answer mathematically. I think I am […]
Question From Inbox: Batteries
Question from inbox: I have a question about problem 3.3 in the original Cram book. My question is regarding the battery charge inefficiency. The problem has 1.2, but should this be 0.2? I am confused where the 1.2 is coming from. Forget the 30A DC motor and let us make the problem more simple. Lets […]
Question From Inbox: Open Delta Transformers
Question from my inbox: I have a question regarding problem 11 of 4.2 Electric Power Devices. The problem is regarding a transformer bank in which one of the banks is removed. The reduced capacity is 57.7% or 288.5 MVA. How do we arrive at this answer? The open delta transformer is identical to a normal […]
Angular Displacement
Three single phase transformers are connected for a three phase application. Given the transformer bank connections below, what is the angular displacement from the high side to the low side? a) 0° b) 30° c) 180° d) 210°
Short-Circuit Problem
A synchronous generator supplies power to a synchronous motor connected directly to its terminals. The sub-transient reactance of the generator and motor on a certain kva base and the rated voltage of the machines are 20 and 100%, respectively. The current supplied by the generator is 80% of base current. The power factor at the […]
Synchronous Machine
A synchronous machine has the three line terminals connected together so that all three phases are in parallel. A single-phase alternating voltage is applied between the line terminals and the neutral terminals with ammeter, A, as shown below. If the test voltage “V” is set equal to 0.55 per unit and the ammeter is reading […]
Power Flow Problem
Given the simple radial system below, if Zline has an angle of 80° and Zload has an angle of 10°, which of the following statements is false? A) As Zload increases, Pr increases rapidly at first and then slowly before reaching a maximum, and finally decreases. B) The power transmitted is maximum when the voltage […]
NEC Question
A commercial warehouse has a 1 phase, 3 wire 120V-240V overhead service connection from the utility to the service panel. The client would like to add a sub panel in the same building for additional circuits. Which diagram below depicts the proper grounding and bonding per the NEC.