Date: 201807
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Dusk
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Electrical Power
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Time Pressure; Workload
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; General Evacuated
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: We departed on Runway XXL. We were climbing in LNAV and VNAV. At 15;000 feet we noticed a burning smell before the Number 2 transfer bus 'Off' light illuminated (generator tripped off). I stated to the First Officer to don his oxygen mask. The flight attendants rang four times. They stated they noticed an odor in the cabin. I stated to the Flight Attendants we would be returning to [the departure airport]. The First Officer lost some flight instruments and gave the aircraft to me. I [advised ATC]. I gave the aircraft back to the First Officer as the situation was realized that it was the generator tripping.I ran the Transfer Off Bus IT Checklist. As I was reading the checklist it called for turning on the APU and restoring the Number 2 transfer bus. I stopped there because I did not want to restore power to a problem. I ran a [Diversion] Checklist. I notified ATC; stating that after landing we needed to go to a disbursement area and deplane using two portable stairs. Also; I requested the fire equipment and personnel.I re-contacted the Flight Attendants and asked how they were and told them we would be on the ground in 10 minutes or less. Then we would taxi to an area very close to the runway. Lastly; we would deplane the passengers via two air stairs; one would pull up at the aft entry and the other the forward entry door. The generator drive light illuminated. I coordinated with Station Operations and Dispatch on the Company frequency. I stated our intentions. I made three announcements to the passengers on the way back to [the departure airport]. The flight attendants; ATC; passengers; Company Operations and Dispatch were notified about our plan.We landed on XXR and made a right turn off the runway. I elected to make a right turn so we were not wedged between two runways. Then I made another right while the APU was starting because I wanted the passengers to leave the aircraft in a safe direction. Once the APU was online I configured for evacuation and shutdown the engines. My First Officer got up to help with the evacuation. I established communication with the Fire Chief. I stated that we wanted the stairs. He stated they only have one set of stairs and it was pulling up to the forward entry door. I made a PA to the passengers that we would be off the aircraft very soon and to follow directions on the ground. Also; I stated to the Flight Attendants to disarm the forward entry door.The Number 2 engine control light illuminated after engine shutdown. The passengers deplaned via stairs and left their luggage on the aircraft. The passengers boarded buses returned to the terminal and were reunited with their bags. The aircraft was de-powered and towed to [the gate]. The passengers departed to [their destination]. One person with asthma discussed their situation with a Paramedic but refused to go to the hospital. A logbook entry was made.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737NG flight crew reported observing caution lights and odors associated with an electrical system anomaly; which necessitated an immediate return to the departure airport; and a passenger evacuation via air stairs.